What is an opposition?

Artist’s concept of Saturn in opposition to the sun. Distances not to scale! Image via NASA.

There has been a lot of talk in this northern summer of 2020 about exciting times for observing Jupiter and Saturn. The two planets are very near each other now on the sky’s dome, heading for a great conjunction before this year’s end. And both reach opposition in July of 2020, Jupiter on July 14 and Saturn on July 20. Opposition marks the middle of the best time of year to view these planets. So … what is an opposition?

Imagine the solar system, with the planets running around in their orbits. Let’s keep things simple and just imagine the sun in the middle with the Earth a little way out, Jupiter about five times farther, and then Saturn about twice as far away from the sun as Jupiter. We’ll assume we’re watching from a spot high above Earth’s North Pole, which would mean that everything is moving counterclockwise.

Now, hit pause. Where are the planets? Maybe Earth is off to the left of the sun, and maybe Jupiter and Saturn are to the right. From this view, it doesn’t really matter what the line from the sun to Earth is like; after all, there’s always a straight line between any two objects in space. But what’s the Earth-sun line doing with respect to, say, Saturn? For most of every year, the Earth-sun line would need to jog off in a different direction to get to Saturn.

If we let our imaginary solar system run a little longer, though, the line will straighten. Nearly every year, there will be a point where it’s perfectly straight – sun, Earth, Saturn – as in the illustration below. Earth will be passing between Saturn and the sun in our planet’s yearly orbit.

An illustration of the solar system – as viewed from Earthly north – on the day of Jupiter’s opposition on July 14, 2020. Earth is passing between Jupiter and the sun on this date. It’ll pass between Saturn and the sun less than a week later, on July 20. In this illustration, the yellow ball in the center (with the central dot) is the sun. Jupiter is brown; Saturn is yellow; Earth is blue. Everything is moving counterclockwise. Image via Fourmilab.

What about the view in Earth’s sky? Since – at opposition – Earth is in the middle of a line between an outer planet and the sun, we see the sun at one end of our sky and the opposition planet in the opposite direction. It’s as if you’re standing directly between two friends as you chat in the supermarket, and you need to turn your head halfway around to see one, and then the other. At opposition, the sun is on the opposite side of the sky from the outer planet; when the sun sets in the west, the planet is rising in the east. As the planet drops below the horizon, the sun pops above it again: opposite.

To be technical, opposition for an outer planet happens when the sun and that planet are exactly 180 degrees apart in the sky. The word comes to English from a Latin root, meaning to set against.

Consider that Venus and Mercury can never be at opposition as seen from Earth. Their orbits are closer to the sun than Earth’s, so they can never appear opposite the sun in our sky. You will never see Venus in the east, for example, when the sun is setting in the west. These inner planets always stay near the sun, no more than 47 degrees from the sun for Venus, or 28 degrees for Mercury, in our sky.

Oppositions can only happen for objects that are farther from the sun than Earth is. We see oppositions for Jupiter, Saturn, Uranus and Neptune about every year. They happen as Earth, in its much-faster orbit, passes between these outer worlds and the sun. We see oppositions of the planet Mars, too, but Martian oppositions happen about every 27 months because Earth and Mars are so relatively close together in orbit around the sun; their orbits, and speeds in orbit, are more similar. We’ll have an opposition of Mars in 2020, too, on October 13. Between now and then, we’ll see Mars brighten dramatically in our sky, as Earth catches up to it, and passes it, on the inside track around the sun.

Since everything in space is always moving, oppositions of planets farther than us from the sun happen again and again. As far as the bright planets go, the next opposition is never too far away:

Mars was at opposition on July 27, 2018, and will be again on October 13, 2020, and December 8, 2022.

Jupiter was at opposition on June 10, 2019, and will be again on July 14, 2020, August 19, 2021, and September 26, 2022.

Saturn was at opposition on July 9, 2019, and will be again on July 20, 2020, August 2, 2021, and August 14, 2022.

View full-sized image. | Project Nightflight released this photo on September 2, 2018. It shows Mars in mid-August of that year, a couple of weeks after its last opposition. See how bright it is? Planets at opposition are bright partly because it’s around then that they are closest to us. Also, at opposition, an outer planet’s fully lighted face, or day side, faces us most directly. Photo via the Project Nightflight team. Read more about this image.

View at EarthSky Community Photos. | Eli Frisbie in Eagle Mountain, Utah, created this composite image from photos gathered on June 6, 2019, just a few days before Jupiter’s opposition. He wrote: “The Milky Way shines over a country road … The bright ‘star’ to the right of the Milky Way is the planet Jupiter. The slightly less-bright star to the upper left is the planet Saturn.” Thank you, Eli!

Why are planets at opposition so interesting to sky-watchers?

As mentioned, because they’re opposite the sun, planets at opposition rise when the sun sets and can be found somewhere in the sky throughout the night.

Secondly, planets at opposition tend to be near their closest point to Earth in orbit. Due to the non-circular shape of planetary orbits, the exact closest point might be different by a day or two, as is the case for Jupiter in 2020. Jupiter’s opposition is on July 14, and its exact closest point is on July 15. Still, for many weeks around opposition – between the time we pass between an outer planet and the sun – the outer planet is generally closest to Earth. At such a time, the planet is brightest, and more detail can be seen through telescopes.

And here’s another interesting aspect of opposition. Since the sun and outer planet are directly opposite each other in Earth’s sky, we see that far-off planet’s fully lighted daytime side. Fully-lit planets appear brighter to us than less-fully-lit planets. If you’re saying to yourself that this sounds a lot like the moon, you’re right! After all, what’s a full moon if not the moon at opposition? During the moon’s full phase, it’s directly opposite the sun in the sky, fully illuminated, and at its brightest for that orbit. As it moves through the rest of its orbit, the sun-Earth-moon line bends and gives us what we see from Earth as the moon’s phases.

Like so much in life, opposition is all about point of view. We’ve been talking about the view from Earth. What if we flip it around? When an outer planet – let’s say Jupiter – is at opposition for us, Earth is at inferior conjunction as seen from that planet. In other words, at the moment of opposition for us on Earth, observers on Jupiter would see Earth passing between their world and the sun. The Earth and the sun would be in the same side of Jupiter’s sky, Earth hidden in the sun’s glare except to skilled observers using special equipment. Consider also that the line from the sun to Jupiter passes through the Earth, which means Earth passes directly between the sun and Jupiter. Maybe one day, a visitor to Jupiter will see Earth transit the sun as seen from Jupiter. That is, they’ll see Earth’s darkened nighttime side, and all of humanity, cross the face of the sun from half a billion miles away.

View at EarthSky Community Photos. | Patrick Prokop in Savannah, Georgia, caught this glorious image of golden Saturn on July 3, 2019, a few days before last year’s opposition. Thank you, Patrick!

Bottom line: Opposition marks the middle of the best time of year to see an outer planet. It’s when Earth is passing between an outer planet and the sun, placing the planet opposite the sun in our sky. A planet at opposition is closest to Earth, and it rises when the sun sets and can be viewed throughout the night.

from EarthSky https://ift.tt/2L8UMSJ

Artist’s concept of Saturn in opposition to the sun. Distances not to scale! Image via NASA.

There has been a lot of talk in this northern summer of 2020 about exciting times for observing Jupiter and Saturn. The two planets are very near each other now on the sky’s dome, heading for a great conjunction before this year’s end. And both reach opposition in July of 2020, Jupiter on July 14 and Saturn on July 20. Opposition marks the middle of the best time of year to view these planets. So … what is an opposition?

Imagine the solar system, with the planets running around in their orbits. Let’s keep things simple and just imagine the sun in the middle with the Earth a little way out, Jupiter about five times farther, and then Saturn about twice as far away from the sun as Jupiter. We’ll assume we’re watching from a spot high above Earth’s North Pole, which would mean that everything is moving counterclockwise.

Now, hit pause. Where are the planets? Maybe Earth is off to the left of the sun, and maybe Jupiter and Saturn are to the right. From this view, it doesn’t really matter what the line from the sun to Earth is like; after all, there’s always a straight line between any two objects in space. But what’s the Earth-sun line doing with respect to, say, Saturn? For most of every year, the Earth-sun line would need to jog off in a different direction to get to Saturn.

If we let our imaginary solar system run a little longer, though, the line will straighten. Nearly every year, there will be a point where it’s perfectly straight – sun, Earth, Saturn – as in the illustration below. Earth will be passing between Saturn and the sun in our planet’s yearly orbit.

An illustration of the solar system – as viewed from Earthly north – on the day of Jupiter’s opposition on July 14, 2020. Earth is passing between Jupiter and the sun on this date. It’ll pass between Saturn and the sun less than a week later, on July 20. In this illustration, the yellow ball in the center (with the central dot) is the sun. Jupiter is brown; Saturn is yellow; Earth is blue. Everything is moving counterclockwise. Image via Fourmilab.

What about the view in Earth’s sky? Since – at opposition – Earth is in the middle of a line between an outer planet and the sun, we see the sun at one end of our sky and the opposition planet in the opposite direction. It’s as if you’re standing directly between two friends as you chat in the supermarket, and you need to turn your head halfway around to see one, and then the other. At opposition, the sun is on the opposite side of the sky from the outer planet; when the sun sets in the west, the planet is rising in the east. As the planet drops below the horizon, the sun pops above it again: opposite.

To be technical, opposition for an outer planet happens when the sun and that planet are exactly 180 degrees apart in the sky. The word comes to English from a Latin root, meaning to set against.

Consider that Venus and Mercury can never be at opposition as seen from Earth. Their orbits are closer to the sun than Earth’s, so they can never appear opposite the sun in our sky. You will never see Venus in the east, for example, when the sun is setting in the west. These inner planets always stay near the sun, no more than 47 degrees from the sun for Venus, or 28 degrees for Mercury, in our sky.

Oppositions can only happen for objects that are farther from the sun than Earth is. We see oppositions for Jupiter, Saturn, Uranus and Neptune about every year. They happen as Earth, in its much-faster orbit, passes between these outer worlds and the sun. We see oppositions of the planet Mars, too, but Martian oppositions happen about every 27 months because Earth and Mars are so relatively close together in orbit around the sun; their orbits, and speeds in orbit, are more similar. We’ll have an opposition of Mars in 2020, too, on October 13. Between now and then, we’ll see Mars brighten dramatically in our sky, as Earth catches up to it, and passes it, on the inside track around the sun.

Since everything in space is always moving, oppositions of planets farther than us from the sun happen again and again. As far as the bright planets go, the next opposition is never too far away:

Mars was at opposition on July 27, 2018, and will be again on October 13, 2020, and December 8, 2022.

Jupiter was at opposition on June 10, 2019, and will be again on July 14, 2020, August 19, 2021, and September 26, 2022.

Saturn was at opposition on July 9, 2019, and will be again on July 20, 2020, August 2, 2021, and August 14, 2022.

View full-sized image. | Project Nightflight released this photo on September 2, 2018. It shows Mars in mid-August of that year, a couple of weeks after its last opposition. See how bright it is? Planets at opposition are bright partly because it’s around then that they are closest to us. Also, at opposition, an outer planet’s fully lighted face, or day side, faces us most directly. Photo via the Project Nightflight team. Read more about this image.

View at EarthSky Community Photos. | Eli Frisbie in Eagle Mountain, Utah, created this composite image from photos gathered on June 6, 2019, just a few days before Jupiter’s opposition. He wrote: “The Milky Way shines over a country road … The bright ‘star’ to the right of the Milky Way is the planet Jupiter. The slightly less-bright star to the upper left is the planet Saturn.” Thank you, Eli!

Why are planets at opposition so interesting to sky-watchers?

As mentioned, because they’re opposite the sun, planets at opposition rise when the sun sets and can be found somewhere in the sky throughout the night.

Secondly, planets at opposition tend to be near their closest point to Earth in orbit. Due to the non-circular shape of planetary orbits, the exact closest point might be different by a day or two, as is the case for Jupiter in 2020. Jupiter’s opposition is on July 14, and its exact closest point is on July 15. Still, for many weeks around opposition – between the time we pass between an outer planet and the sun – the outer planet is generally closest to Earth. At such a time, the planet is brightest, and more detail can be seen through telescopes.

And here’s another interesting aspect of opposition. Since the sun and outer planet are directly opposite each other in Earth’s sky, we see that far-off planet’s fully lighted daytime side. Fully-lit planets appear brighter to us than less-fully-lit planets. If you’re saying to yourself that this sounds a lot like the moon, you’re right! After all, what’s a full moon if not the moon at opposition? During the moon’s full phase, it’s directly opposite the sun in the sky, fully illuminated, and at its brightest for that orbit. As it moves through the rest of its orbit, the sun-Earth-moon line bends and gives us what we see from Earth as the moon’s phases.

Like so much in life, opposition is all about point of view. We’ve been talking about the view from Earth. What if we flip it around? When an outer planet – let’s say Jupiter – is at opposition for us, Earth is at inferior conjunction as seen from that planet. In other words, at the moment of opposition for us on Earth, observers on Jupiter would see Earth passing between their world and the sun. The Earth and the sun would be in the same side of Jupiter’s sky, Earth hidden in the sun’s glare except to skilled observers using special equipment. Consider also that the line from the sun to Jupiter passes through the Earth, which means Earth passes directly between the sun and Jupiter. Maybe one day, a visitor to Jupiter will see Earth transit the sun as seen from Jupiter. That is, they’ll see Earth’s darkened nighttime side, and all of humanity, cross the face of the sun from half a billion miles away.

View at EarthSky Community Photos. | Patrick Prokop in Savannah, Georgia, caught this glorious image of golden Saturn on July 3, 2019, a few days before last year’s opposition. Thank you, Patrick!

Bottom line: Opposition marks the middle of the best time of year to see an outer planet. It’s when Earth is passing between an outer planet and the sun, placing the planet opposite the sun in our sky. A planet at opposition is closest to Earth, and it rises when the sun sets and can be viewed throughout the night.

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Moon and Mars before dawn June 12 and 13

In the predawn sky these next few mornings – June 12 and 13, 2020 – use the waning crescent moon to find the red planet Mars. Look first for the moon. That nearby bright “star” will be Mars. Unlike a star, which shines by its own light, Mars shines by reflecting the light of the sun. You may note that Mars shines with a steadier light than the twinkling stars. And, if you’ve been watching, you’ll also notice how bright Mars is now! The planet is due to grow dramatically brighter by the time of its opposition – when Earth will fly between Mars and the sun – in October 2020.

At mid-northern latitudes, it’s now that beautiful time of year when we’re having our earliest sunrises. So northerners might be hard pressed to get up early enough to see the moon and Mars. If you’re a night owl, staying up past the midnight hour, you might try to catch the pair rising into your eastern sky before bedtime.

Live in the United States or Canada? Click on Old Farmer’s Almanac to find out the rising times of the moon and Mars.

To find out the rising times for the moon and Mars from virtually anyplace worldwide, check out TimeandDate.

On our chart at top, we also show the planet Neptune, the most distant (known) planet in our the solar system. You need an optical aid to see this distant world. Mars and Neptune will be in conjunction on June 12, 2020 (at about 12:00 UTC), with Mars passing 1.7 degrees to the south of Neptune. For reference, your index finger at arm’s length spans about 2 degrees of sky.

About half a day after the Mars-Neptune conjunction, the moon will pass 3 degrees to the south of Mars. Then about a quarter day after the moon meets up with Mars, the moon will reach its half-illuminated last quarter phase on June 13, 2020, at 6:24 UTC.

Earth is gaining on Mars in our faster, smaller orbit around the sun, and Mars, in turn, is growing ever brighter in Earth’s sky. Excluding our sun, only three stars are brighter than Mars at present: Sirius, Canopus and Alpha Centauri. Mars outshines Neptune by nearly 1,700 times, and the 1st-magnitude star Fomalhaut by nearly 3.5 times.

Yet, the great Mars show has barely begun. By the second half of August 2020, Mars will actually outshine Sirius, the brightest star of the nighttime sky. By October 2020, Mars will even outshine the king planet Jupiter. Jupiter is almost always the fourth-brightest celestial body, after the sun, moon and the queen planet Venus. But, Mars will displace Jupiter for one shining month, as Mars beams as the fourth-brightest celestial object, after the sun, moon and Venus, throughout October 2020.

Two other morning planets light up the June 2020 predawn/dawn sky. Look for the king planet Jupiter and the ringed planet Saturn to the west of the moon and Mars. Note: the moon appears much larger on our chart than it does in the real sky.

During these these few mornings – June 12 and 13, 2020 – the moon, Mars and Neptune appear close together on the sky’s dome, but they’re hardly close together in space. The moon lies about a quarter million miles (400,000 km) away from Earth. In contrast, Mars resides at better than 350 times the moon’s distance from Earth. Meanwhile, Neptune lodges way out there, at some 32 times Mars’ distance from Earth.

Bottom line: Enjoy the early morning sky on June 12 and 13, 2020, as the moon swings 3 degrees south of the red planet Mars, and Mars swings 1.7 degrees south of Neptune.

from EarthSky https://ift.tt/3ho2V2D

In the predawn sky these next few mornings – June 12 and 13, 2020 – use the waning crescent moon to find the red planet Mars. Look first for the moon. That nearby bright “star” will be Mars. Unlike a star, which shines by its own light, Mars shines by reflecting the light of the sun. You may note that Mars shines with a steadier light than the twinkling stars. And, if you’ve been watching, you’ll also notice how bright Mars is now! The planet is due to grow dramatically brighter by the time of its opposition – when Earth will fly between Mars and the sun – in October 2020.

At mid-northern latitudes, it’s now that beautiful time of year when we’re having our earliest sunrises. So northerners might be hard pressed to get up early enough to see the moon and Mars. If you’re a night owl, staying up past the midnight hour, you might try to catch the pair rising into your eastern sky before bedtime.

Live in the United States or Canada? Click on Old Farmer’s Almanac to find out the rising times of the moon and Mars.

To find out the rising times for the moon and Mars from virtually anyplace worldwide, check out TimeandDate.

On our chart at top, we also show the planet Neptune, the most distant (known) planet in our the solar system. You need an optical aid to see this distant world. Mars and Neptune will be in conjunction on June 12, 2020 (at about 12:00 UTC), with Mars passing 1.7 degrees to the south of Neptune. For reference, your index finger at arm’s length spans about 2 degrees of sky.

About half a day after the Mars-Neptune conjunction, the moon will pass 3 degrees to the south of Mars. Then about a quarter day after the moon meets up with Mars, the moon will reach its half-illuminated last quarter phase on June 13, 2020, at 6:24 UTC.

Earth is gaining on Mars in our faster, smaller orbit around the sun, and Mars, in turn, is growing ever brighter in Earth’s sky. Excluding our sun, only three stars are brighter than Mars at present: Sirius, Canopus and Alpha Centauri. Mars outshines Neptune by nearly 1,700 times, and the 1st-magnitude star Fomalhaut by nearly 3.5 times.

Yet, the great Mars show has barely begun. By the second half of August 2020, Mars will actually outshine Sirius, the brightest star of the nighttime sky. By October 2020, Mars will even outshine the king planet Jupiter. Jupiter is almost always the fourth-brightest celestial body, after the sun, moon and the queen planet Venus. But, Mars will displace Jupiter for one shining month, as Mars beams as the fourth-brightest celestial object, after the sun, moon and Venus, throughout October 2020.

Two other morning planets light up the June 2020 predawn/dawn sky. Look for the king planet Jupiter and the ringed planet Saturn to the west of the moon and Mars. Note: the moon appears much larger on our chart than it does in the real sky.

During these these few mornings – June 12 and 13, 2020 – the moon, Mars and Neptune appear close together on the sky’s dome, but they’re hardly close together in space. The moon lies about a quarter million miles (400,000 km) away from Earth. In contrast, Mars resides at better than 350 times the moon’s distance from Earth. Meanwhile, Neptune lodges way out there, at some 32 times Mars’ distance from Earth.

Bottom line: Enjoy the early morning sky on June 12 and 13, 2020, as the moon swings 3 degrees south of the red planet Mars, and Mars swings 1.7 degrees south of Neptune.

from EarthSky https://ift.tt/3ho2V2D

Scientists to strike on June 10 #ShutDownSTEM #Strike4BlackLives

Image via ScienceMag.org, a publication of the American Association for the Advancement of Science, which has also endorsed the strike.

Thousands of physicists, astronomers, and other academics have pledged to pause their work – forgoing research, classes, meetings, and other normal business – on Wednesday, June 10, 2020, in order to pursue a day of action dedicated to protecting the lives of Black people. The strike is taking place due to the efforts of multiple organizers operating under banners including the Strike For Black Lives, #ShutDownSTEM, #ShutDownAcademia and #Strike4BlackLives. A group of 15 physicist organizers wrote on the website Particles for Justice that the Strike for Black Lives is needed to:

… hit pause, to give Black academics a break and to give others an opportunity to reflect on their own complicity in anti-Black racism in academia and their local and global communities.

Chanda Prescod-Weinstein, a particle cosmology theorist and feminist theorist at the University of New Hampshire, said:

I want non-Black people to respond as if lives depend on it because they do.

The organizers of #ShutDownSTEM state on its website:

In the wake of the most recent murders of Black people in the U.S., it is clear that white and other non-Black people have to step up and do the work to eradicate anti-Black racism. As members of the global academic and STEM [science, technology, engineering, and math] communities, we have an enormous ethical obligation to stop doing ‘business as usual.’

More information:

https://www.particlesforjustice.org

https://www.shutdownstem.com

https://www.aip.org/fyi/2020/scientists-strike-black-lives-shutdownstem-june-10

https://aas.org/posts/news/2020/06/aas-endorses-shutdownstem-shutdownacademia-strike4blacklives

Resources for #ShutDownSTEM, #ShutDownAcademia & #Strike4BlackLives:
https://aas.org/strike4blacklives

Bottom line: University laboratories, scientific societies, technical journals, and others have pledged to strike on June 10, 2020. The focus is on issues of racial equality and inclusiveness. The strike is taking place under multiple banners including the Strike For Black Lives, #ShutDownSTEM, #ShutDownAcademia, and #Strike4BlackLives. EarthSky is joining the strike.

from EarthSky https://ift.tt/2MOSYNe

Image via ScienceMag.org, a publication of the American Association for the Advancement of Science, which has also endorsed the strike.

Thousands of physicists, astronomers, and other academics have pledged to pause their work – forgoing research, classes, meetings, and other normal business – on Wednesday, June 10, 2020, in order to pursue a day of action dedicated to protecting the lives of Black people. The strike is taking place due to the efforts of multiple organizers operating under banners including the Strike For Black Lives, #ShutDownSTEM, #ShutDownAcademia and #Strike4BlackLives. A group of 15 physicist organizers wrote on the website Particles for Justice that the Strike for Black Lives is needed to:

… hit pause, to give Black academics a break and to give others an opportunity to reflect on their own complicity in anti-Black racism in academia and their local and global communities.

Chanda Prescod-Weinstein, a particle cosmology theorist and feminist theorist at the University of New Hampshire, said:

I want non-Black people to respond as if lives depend on it because they do.

The organizers of #ShutDownSTEM state on its website:

In the wake of the most recent murders of Black people in the U.S., it is clear that white and other non-Black people have to step up and do the work to eradicate anti-Black racism. As members of the global academic and STEM [science, technology, engineering, and math] communities, we have an enormous ethical obligation to stop doing ‘business as usual.’

More information:

https://www.particlesforjustice.org

https://www.shutdownstem.com

https://www.aip.org/fyi/2020/scientists-strike-black-lives-shutdownstem-june-10

https://aas.org/posts/news/2020/06/aas-endorses-shutdownstem-shutdownacademia-strike4blacklives

Resources for #ShutDownSTEM, #ShutDownAcademia & #Strike4BlackLives:
https://aas.org/strike4blacklives

Bottom line: University laboratories, scientific societies, technical journals, and others have pledged to strike on June 10, 2020. The focus is on issues of racial equality and inclusiveness. The strike is taking place under multiple banners including the Strike For Black Lives, #ShutDownSTEM, #ShutDownAcademia, and #Strike4BlackLives. EarthSky is joining the strike.

from EarthSky https://ift.tt/2MOSYNe

Evolution: Why it seems to have a direction, and what to expect next

Is intelligent life bad news for diversity? Image via Gudkov Andrey/ Shutterstock.

Matthew Wills, University of Bath

The diversity and complexity of life on Earth is astonishing: 8 million or more living species – from algae to elephants – all evolved from a simple, single-celled common ancestor around 3.5 billion years ago. But does that mean that evolution always and inevitably generates greater diversity and complexity, having a predictable direction?

Charles Darwin identified three ingredients necessary for natural selection to occur. Individuals must be different, so there is variation in the population. They must also be able to pass this variation on to offspring. Finally, individuals must compete for resources that limit the number of offspring they can produce. Individuals with variations that allow them to obtain more resources are likely to produce more offspring like themselves.

Evolution also depends on context and environment, which notoriously change constantly in unpredictable ways. For example, fishes who start living and evolving in unlit caves often lose their eyes, because the costs of developing them outweigh their advantages.

Blind cave fish. Image via wikipedia

So natural selection operates from one generation to the next. It cannot plan ahead or have a goal. In addition, not all evolutionary change is a response to selection, but can be neutral or random. It is not even guaranteed to produce more species, since evolution can occur in a single lineage and this can go extinct at any time. How can we reconcile such an aimless process with the bewildering diversity and complexity we see?

Ecological influence

Ecology and evolution are two sides of the same coin. The environment is not just the physical surroundings of an organism, but also the other biological species with which it interacts.

We can see this environmental interaction deep in the history of life. For billions of years, organisms were “stuck” as single cells within the seas. Several groups independently evolved multi-cellularity (perhaps 25 times). But the first animals, plants and fungi with complex development, different tissues and organs only appeared around 540 million years ago, with the Cambrian “explosion” of diversity.

This may have been triggered by increased levels of oxygen in the oceans, which was, in turn, the result of photosynthesis – the process by which plants and other organisms convert sunlight into energy while releasing oxygen – in much simpler forms of life over millions of years.

Once animals had attained greater size and evolved guts, hard parts, jaws, teeth, eyes and legs, complex food webs became possible – along with “arms races” between predators and prey. Groups with adaptations that enabled them to live on land opened up even more opportunities. Once out of the bag, these innovations were difficult to “uninvent” – promoting diversity.

The only diagram in Darwin’s On the Origin of Species shows species splitting through time. If more species originate than go extinct, then species richness increases. Darwin wondered whether ecological space might simply “fill up” one day.

Diagram from On the Origin of Species. Image via Wikipedia.

But so far as we can tell, the species count has been increasing for most of the last 250 million years. Even past natural mass extinctions were only temporary setbacks that may have created even more opportunities for diversity in the long run.

Variation is not random

As organisms evolve more complicated systems of development, they may, however, become less able to modify certain aspects of their anatomy. This is partly because genes, tissues and organs often have several different functions, so it may become difficult to change one for the better without accidentally “breaking” something elsewhere.

For example, nearly all mammals – from giraffes to humans – are stuck with just seven neck bones. Whenever different numbers develop or evolve, they bring other anatomical problems. Birds are entirely different, and seem to evolve new numbers of neck vertebrae with remarkable ease: Swans alone have between 22 and 25. But in general, while evolution produces new species, the flexibility of the body plans of those species may decrease with rising complexity.

Giraffes have 7 neck bones. Image via John Michael Vosloo/ Shutterstock.

Quite often, closely related species end up being selected along similar paths. Moreover, “developmental bias” means that anatomical variation is not produced at random.

Take mammals. They come from a common ancestor, and have taken strikingly similar forms even though they have evolved on different continents. This is another example of the fact that evolution isn’t entirely unpredictable – there are only so many solutions to the same physical and biological problems, like seeing, digging or flying.

The future of evolution

Clearly, there is an apparent contradiction at the heart of evolutionary biology. On one hand, the mechanisms of evolution have no predisposition for change in any particular direction. On the other hand, let those mechanisms get going, and beyond some threshold, the interwoven ecological and developmental systems they generate tend to yield more and more species with greater maximum complexity.

So can we expect more diversity and complexity going forward? We are now at the beginning of a sixth mass extinction, caused by humans and showing no signs of stopping – wiping out the results of millions of years of evolution. Despite this, humans themselves are too numerous, widespread and adaptable to be at serious risk of extinction any time soon. It is far more likely that we will extend our distribution yet further by engineering habitable biospheres on other planets.

On other planets, we may one day find alien life. Would that follow the same evolutionary trajectory as life on Earth? From one cell, the transition to multi-cellularity may be an easy hurdle to jump. Although it came quite late on Earth, it nevertheless happened many times. More complicated development with different tissue types evolved in only a few groups on Earth, so may represent a higher bar.

If alien biology makes it over some hurdles, its development is indeed likely to favor patterns of increasing diversity and maximum complexity. But perhaps a dominant, intelligent species like humans will always be bad news for many of the other species on the planets where they evolve.

The astronomer Frank Drake proposed an equation to estimate how many intelligent civilizations we might expect in our galaxy. This contained a term for how long such civilizations might exist before destroying themselves. Drake was pessimistic about this: let’s hope he was wrong.

Matthew Wills, Professor of Evolutionary Palaeobiology at the Milner Centre for Evolution, University of Bath

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Bottom line: Why evolution seems to have a direction, and what to expect next.

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Is intelligent life bad news for diversity? Image via Gudkov Andrey/ Shutterstock.

Matthew Wills, University of Bath

The diversity and complexity of life on Earth is astonishing: 8 million or more living species – from algae to elephants – all evolved from a simple, single-celled common ancestor around 3.5 billion years ago. But does that mean that evolution always and inevitably generates greater diversity and complexity, having a predictable direction?

Charles Darwin identified three ingredients necessary for natural selection to occur. Individuals must be different, so there is variation in the population. They must also be able to pass this variation on to offspring. Finally, individuals must compete for resources that limit the number of offspring they can produce. Individuals with variations that allow them to obtain more resources are likely to produce more offspring like themselves.

Evolution also depends on context and environment, which notoriously change constantly in unpredictable ways. For example, fishes who start living and evolving in unlit caves often lose their eyes, because the costs of developing them outweigh their advantages.

Blind cave fish. Image via wikipedia

So natural selection operates from one generation to the next. It cannot plan ahead or have a goal. In addition, not all evolutionary change is a response to selection, but can be neutral or random. It is not even guaranteed to produce more species, since evolution can occur in a single lineage and this can go extinct at any time. How can we reconcile such an aimless process with the bewildering diversity and complexity we see?

Ecological influence

Ecology and evolution are two sides of the same coin. The environment is not just the physical surroundings of an organism, but also the other biological species with which it interacts.

We can see this environmental interaction deep in the history of life. For billions of years, organisms were “stuck” as single cells within the seas. Several groups independently evolved multi-cellularity (perhaps 25 times). But the first animals, plants and fungi with complex development, different tissues and organs only appeared around 540 million years ago, with the Cambrian “explosion” of diversity.

This may have been triggered by increased levels of oxygen in the oceans, which was, in turn, the result of photosynthesis – the process by which plants and other organisms convert sunlight into energy while releasing oxygen – in much simpler forms of life over millions of years.

Once animals had attained greater size and evolved guts, hard parts, jaws, teeth, eyes and legs, complex food webs became possible – along with “arms races” between predators and prey. Groups with adaptations that enabled them to live on land opened up even more opportunities. Once out of the bag, these innovations were difficult to “uninvent” – promoting diversity.

The only diagram in Darwin’s On the Origin of Species shows species splitting through time. If more species originate than go extinct, then species richness increases. Darwin wondered whether ecological space might simply “fill up” one day.

Diagram from On the Origin of Species. Image via Wikipedia.

But so far as we can tell, the species count has been increasing for most of the last 250 million years. Even past natural mass extinctions were only temporary setbacks that may have created even more opportunities for diversity in the long run.

Variation is not random

As organisms evolve more complicated systems of development, they may, however, become less able to modify certain aspects of their anatomy. This is partly because genes, tissues and organs often have several different functions, so it may become difficult to change one for the better without accidentally “breaking” something elsewhere.

For example, nearly all mammals – from giraffes to humans – are stuck with just seven neck bones. Whenever different numbers develop or evolve, they bring other anatomical problems. Birds are entirely different, and seem to evolve new numbers of neck vertebrae with remarkable ease: Swans alone have between 22 and 25. But in general, while evolution produces new species, the flexibility of the body plans of those species may decrease with rising complexity.

Giraffes have 7 neck bones. Image via John Michael Vosloo/ Shutterstock.

Quite often, closely related species end up being selected along similar paths. Moreover, “developmental bias” means that anatomical variation is not produced at random.

Take mammals. They come from a common ancestor, and have taken strikingly similar forms even though they have evolved on different continents. This is another example of the fact that evolution isn’t entirely unpredictable – there are only so many solutions to the same physical and biological problems, like seeing, digging or flying.

The future of evolution

Clearly, there is an apparent contradiction at the heart of evolutionary biology. On one hand, the mechanisms of evolution have no predisposition for change in any particular direction. On the other hand, let those mechanisms get going, and beyond some threshold, the interwoven ecological and developmental systems they generate tend to yield more and more species with greater maximum complexity.

So can we expect more diversity and complexity going forward? We are now at the beginning of a sixth mass extinction, caused by humans and showing no signs of stopping – wiping out the results of millions of years of evolution. Despite this, humans themselves are too numerous, widespread and adaptable to be at serious risk of extinction any time soon. It is far more likely that we will extend our distribution yet further by engineering habitable biospheres on other planets.

On other planets, we may one day find alien life. Would that follow the same evolutionary trajectory as life on Earth? From one cell, the transition to multi-cellularity may be an easy hurdle to jump. Although it came quite late on Earth, it nevertheless happened many times. More complicated development with different tissue types evolved in only a few groups on Earth, so may represent a higher bar.

If alien biology makes it over some hurdles, its development is indeed likely to favor patterns of increasing diversity and maximum complexity. But perhaps a dominant, intelligent species like humans will always be bad news for many of the other species on the planets where they evolve.

The astronomer Frank Drake proposed an equation to estimate how many intelligent civilizations we might expect in our galaxy. This contained a term for how long such civilizations might exist before destroying themselves. Drake was pessimistic about this: let’s hope he was wrong.

Matthew Wills, Professor of Evolutionary Palaeobiology at the Milner Centre for Evolution, University of Bath

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Bottom line: Why evolution seems to have a direction, and what to expect next.

from EarthSky https://ift.tt/30tHlDy

Find the Crow, Cup and Water Snake

At nightfall tonight, or any June evening, look in a general southward direction for Spica, the brightest star in the constellation Virgo the Maiden. If you live in the Southern Hemisphere, Spica appears overhead or high in your northern sky around 9 p.m. in early June. Spica is your jumping off point to three faint constellations: Corvus the Crow, Crater the Cup and Hydra the Snake.

If you’re familiar with the Big Dipper, use this signpost star formation to star-hop to Spica, as shown in the sky chart below:

Use the Big Dipper to arc to Arcturus and spike Spica. Read more.

You can use Spica to find the constellation Corvus – and alternately, use Corvus to confirm that you’ve found Spica:

Here’s another way to verify that you’re looking at Spica, the brightest star in the constellation Virgo.

Okay … got Spica? Now, as nightfall deepens into later evening, watch for a number of fainter stars to become visible. That’s when the Crow, the Cup and the Water Snake will come into view.

Sky chart of the constellation Hydra, including Corvus and the Crater via IAU.

In Greek mythology, Apollo sent the crow to fetch a cup of water. The crow, Corvus, got distracted eating figs. It was only after much delay that he finally remembered his mission. Rightly figuring that Apollo would be angry, the crow plucked a snake from the water and concocted a story about how it had attacked and delayed him.

Hydra the Water Snake with the orange star Alphard at its heart. Illustration via Deanspace.

Apollo was not fooled and angrily flung the Crow, Cup and Snake into the sky, placing the Crow and Cup on the Snake’s back.

Then the god ordered Hydra to never let the Crow drink from the Cup. As a further punishment, he ordered that the Crow could never sing again, only screech and caw.

None of these constellations has any bright stars, but Hydra holds the distinction of being the longest constellation in the heavens.

Bottom line: Use the bright star Spica to help you find the constellations Corvus the Crow, Crater the Cup, and Hydra the Water Snake.

Enjoying EarthSky so far? Sign up for our free daily newsletter today!

from EarthSky https://ift.tt/3dQPW74

At nightfall tonight, or any June evening, look in a general southward direction for Spica, the brightest star in the constellation Virgo the Maiden. If you live in the Southern Hemisphere, Spica appears overhead or high in your northern sky around 9 p.m. in early June. Spica is your jumping off point to three faint constellations: Corvus the Crow, Crater the Cup and Hydra the Snake.

If you’re familiar with the Big Dipper, use this signpost star formation to star-hop to Spica, as shown in the sky chart below:

Use the Big Dipper to arc to Arcturus and spike Spica. Read more.

You can use Spica to find the constellation Corvus – and alternately, use Corvus to confirm that you’ve found Spica:

Here’s another way to verify that you’re looking at Spica, the brightest star in the constellation Virgo.

Okay … got Spica? Now, as nightfall deepens into later evening, watch for a number of fainter stars to become visible. That’s when the Crow, the Cup and the Water Snake will come into view.

Sky chart of the constellation Hydra, including Corvus and the Crater via IAU.

In Greek mythology, Apollo sent the crow to fetch a cup of water. The crow, Corvus, got distracted eating figs. It was only after much delay that he finally remembered his mission. Rightly figuring that Apollo would be angry, the crow plucked a snake from the water and concocted a story about how it had attacked and delayed him.

Hydra the Water Snake with the orange star Alphard at its heart. Illustration via Deanspace.

Apollo was not fooled and angrily flung the Crow, Cup and Snake into the sky, placing the Crow and Cup on the Snake’s back.

Then the god ordered Hydra to never let the Crow drink from the Cup. As a further punishment, he ordered that the Crow could never sing again, only screech and caw.

None of these constellations has any bright stars, but Hydra holds the distinction of being the longest constellation in the heavens.

Bottom line: Use the bright star Spica to help you find the constellations Corvus the Crow, Crater the Cup, and Hydra the Water Snake.

Enjoying EarthSky so far? Sign up for our free daily newsletter today!

from EarthSky https://ift.tt/3dQPW74

Big and Little Dippers on June evenings

Tonight, assuming you’re in the Northern Hemisphere, you can easily find the legendary Big Dipper, called The Plough by our friends in the U.K. or The Wagon throughout much of Europe. This familiar star pattern is high in the north at nightfall in June. Find it, and let it be your guide to the Little Dipper, too.

You can find the Big Dipper easily because its shape really resembles a dipper. Meanwhile, the Little Dipper isn’t as easy to find. You need a dark sky to see the Little Dipper, so be sure to avoid city lights.

How do you find the Dippers? Assuming you’re in the Northern Hemisphere, simply face northward on a June evening, and watch for a large dipper-like pattern. That easy-to-see pattern will be the Big Dipper. Notice that the Big Dipper has two parts: a bowl and a handle. See the two outer stars in the bowl? They’re known as The Pointers because they point to the North Star, which is also known as Polaris.

Once you’ve found Polaris, you can find the Little Dipper. Polaris marks the end of the handle of the Little Dipper. You need a dark night to see the Little Dipper in full, because it’s so much fainter than its larger and brighter counterpart.

By the way, can you see the Big Dipper from Earth’s Southern Hemisphere? Yes, if you’re in the southern tropics. Much farther south, and it gets harder because as you go southward on Earth’s globe, the Dipper sinks closer and closer to the northern horizon.

Meanwhile, Polaris, the North Star, disappears beneath the horizon once you get south of the Earth’s equator.

The Big and Little Dippers aren’t constellations. They’re asterisms, or noticeable star patterns. The Big Dipper is part of Ursa Major the Greater Bear. The Little Dipper belongs to Ursa Minor the Lesser Bear.

In his classic book “Star Names: Their Lore and Meaning,” Richard Hinckley Allen claims the Greek constellation Ursa Minor was never mentioned in the literary works of Homer (9th century B.C.) or Hesiod (8th century B.C.). That’s probably because this constellation hadn’t been invented yet, that long ago.

According to the Greek geographer and historian Strabo (63 B.C. to A.D. 21?), the seven stars we see today as part of Ursa Minor (the Little Dipper) didn’t carry that name until 600 B.C. or so. Before that time, people saw this group of stars outlining the wings of the constellation Draco the Dragon.

When the seafaring Phoenicians visited the Greek philosopher Thales around 600 B.C., they showed him how to navigate by the stars. Purportedly, Thales clipped the Dragon’s wings to create a new constellation, possibly because this new way of looking at the stars enabled Greek sailors to more easily locate the north celestial pole.

But it’s not just our names for things in the sky that change. The sky itself changes, too. In our day, Polaris closely marks the north celestial pole in the sky. In 600 B.C. – thanks to the motion of precession – the stars Kochab and Pherkad more closely marked the position of the north celestial pole.

Kochab and Pherkad: Guardians of the Pole

No matter what time of night it is – or what time of year it is – in other words, no matter how the Big Dipper is oriented in the sky, the 2 outer stars in its bowl always point to Polaris, the North Star. Image by EarthSky Facebook friend Abhijit Juvekar.

Bottom line: Look for the Big and Little Dippers in the north at nightfall!

Help EarthSky keep going! Please donate.

EarthSky astronomy kits are perfect for beginners. Order today from the EarthSky store

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Tonight, assuming you’re in the Northern Hemisphere, you can easily find the legendary Big Dipper, called The Plough by our friends in the U.K. or The Wagon throughout much of Europe. This familiar star pattern is high in the north at nightfall in June. Find it, and let it be your guide to the Little Dipper, too.

You can find the Big Dipper easily because its shape really resembles a dipper. Meanwhile, the Little Dipper isn’t as easy to find. You need a dark sky to see the Little Dipper, so be sure to avoid city lights.

How do you find the Dippers? Assuming you’re in the Northern Hemisphere, simply face northward on a June evening, and watch for a large dipper-like pattern. That easy-to-see pattern will be the Big Dipper. Notice that the Big Dipper has two parts: a bowl and a handle. See the two outer stars in the bowl? They’re known as The Pointers because they point to the North Star, which is also known as Polaris.

Once you’ve found Polaris, you can find the Little Dipper. Polaris marks the end of the handle of the Little Dipper. You need a dark night to see the Little Dipper in full, because it’s so much fainter than its larger and brighter counterpart.

By the way, can you see the Big Dipper from Earth’s Southern Hemisphere? Yes, if you’re in the southern tropics. Much farther south, and it gets harder because as you go southward on Earth’s globe, the Dipper sinks closer and closer to the northern horizon.

Meanwhile, Polaris, the North Star, disappears beneath the horizon once you get south of the Earth’s equator.

The Big and Little Dippers aren’t constellations. They’re asterisms, or noticeable star patterns. The Big Dipper is part of Ursa Major the Greater Bear. The Little Dipper belongs to Ursa Minor the Lesser Bear.

In his classic book “Star Names: Their Lore and Meaning,” Richard Hinckley Allen claims the Greek constellation Ursa Minor was never mentioned in the literary works of Homer (9th century B.C.) or Hesiod (8th century B.C.). That’s probably because this constellation hadn’t been invented yet, that long ago.

According to the Greek geographer and historian Strabo (63 B.C. to A.D. 21?), the seven stars we see today as part of Ursa Minor (the Little Dipper) didn’t carry that name until 600 B.C. or so. Before that time, people saw this group of stars outlining the wings of the constellation Draco the Dragon.

When the seafaring Phoenicians visited the Greek philosopher Thales around 600 B.C., they showed him how to navigate by the stars. Purportedly, Thales clipped the Dragon’s wings to create a new constellation, possibly because this new way of looking at the stars enabled Greek sailors to more easily locate the north celestial pole.

But it’s not just our names for things in the sky that change. The sky itself changes, too. In our day, Polaris closely marks the north celestial pole in the sky. In 600 B.C. – thanks to the motion of precession – the stars Kochab and Pherkad more closely marked the position of the north celestial pole.

Kochab and Pherkad: Guardians of the Pole

No matter what time of night it is – or what time of year it is – in other words, no matter how the Big Dipper is oriented in the sky, the 2 outer stars in its bowl always point to Polaris, the North Star. Image by EarthSky Facebook friend Abhijit Juvekar.

Bottom line: Look for the Big and Little Dippers in the north at nightfall!

Help EarthSky keep going! Please donate.

EarthSky astronomy kits are perfect for beginners. Order today from the EarthSky store

from EarthSky https://ift.tt/3dMXzeX

A 2nd exoplanet confirmed for Proxima Centauri

Artist’s concept of Proxima Centauri b and c – depicted here as 2 black dots, a larger one and a smaller one – orbiting their red dwarf star. Proxima Centauri c, the larger planet, might also have a ring system. Image via Michele Diodati/ Medium.

Just a few days ago, scientists announced that the closest known Earth-sized exoplanet, Proxima Centauri b, had been confirmed to orbit the nearest star to our solar system. That’s an exciting development, but now, as scientists announced on June 2, 2020, it seems that another possible planet around the same star also has been verified … Proxima Centauri c! Both planets are only 4.2 light-years away.

The peer-reviewed results were published in Research Notes of the AAS back in April. Astronomer Fritz Benedict of McDonald Observatory presented the findings at the virtual 236th meeting of the American Astronomical Society.

Evidence for Proxima Centauri c was first announced earlier this year by a research group led by Mario Damasso of Italy’s National Institute for Astrophysics (INAF). But the evidence wasn’t conclusive. This second planet for Proxima is apparently a lot larger than Earth and orbits its star every 1,907 days. It orbits at about 1.5 times the distance from its star that Earth orbits from the sun. Not an extreme difference, but Proxima Centauri is a red dwarf star, smaller and cooler than our sun, so at that distance, the planet can be expected to be significantly colder than Earth.

Combined images from the SPHERE instrument on the Very Large Telescope (VLT) in Chile, which appear to show Proxima Centauri c as a bright dot. The location is right where the planet was predicted to be in its orbit. The star is hidden behind the black circle in the center. Image via Gratton et al./ A&A/ Nature Astronomy.

Even though Proxima Centauri is the closest star to the sun, it’s difficult to detect the planets orbiting it. Most exoplanets have been found via the transit method, and this system isn’t oriented with respect to Earth such that its planets transit in front of Proxima, from our perspective. So scientists have to use radial velocity observations, measurements of Proxima’s motion toward and away from Earth, to detect the tiny effects of the planets’ gravitational tuggings on the star.

Benedict’s idea was to look again at previous studies of the star from the 1990s from the Hubble Space Telescope (HST), which used the telescope’s Fine Guidance Sensors (FGS). The FGS can be used for astrometry, where scientists can take very accurate measurements of the positions and motions of objects in the sky. If Proxima Centauri c were really there, FGS should be able to detect it. Benedict said in a statement:

Basically, this is a story of how old data can be very useful when you get new information. It’s also a story of how hard it is to retire if you’re an astronomer, because this is fun stuff to do!

So what did Benedict and his team find?

When they looked at the old Hubble data, they found a planet with an orbital period of 1,907 days, which fit with what had been seen before, for the tentative Proxima Centauri c. The planet had been overlooked before because in the 1990s, researchers only checked the data for planets with orbital periods of less than 1,000 days.

Benedict combined the results of three studies: the Hubble/FGS astrometry, the radial velocity studies and images from the SPHERE instrument on the Very Large Telescope (VLT) in Chile, to better estimate the mass of Proxima Centauri c. He concluded that the planet is approximately seven times more massive than Earth.

Size comparison of the three stars in the Alpha Centauri system, including Proxima Centauri, and the sun. Image via PHL @ UPR Arecibo.

Proxima Centauri is the closest of the three stars in the Alpha Centauri system. Image via ESO/ BBC.

Earlier this year, scientists using the images from SPHERE found what appeared to be a large planet orbiting Proxima Centauri that coincided with the predicted position of Proxima Centauri c at the time.

But based on those images, it was found that Proxima Centauri c appeared to be brighter than expected. If the brightness was entirely from the light reflected off the planet itself, then the planet would be about five times larger than Jupiter. But since its estimated mass is more similar to Neptune’s, it may actually be smaller, but has dust clouds or a huge ring system around it. Determining whether it actually does or not will require more observations. It is bright enough that better images of it should be able to be taken by upcoming space telescopes. That’s not the case, unfortunately, with Proxima Centauri b, since it is smaller and much closer to the star. From another recent paper:

Proxima c could become a prime target for follow-up and characterization with next-generation direct imaging instrumentation due to the large maximum angular separation of ~1 arc second from the parent star. The candidate planet represents a challenge for the models of super-Earth formation and evolution.

As far as possible life is concerned, Proxima Centauri c may be too cold for life as we know it, but we just don’t know enough about it yet. Proxima Centauri b is a better candidate for being potentially habitable, since it is only slightly larger than Earth, orbits in the habitable zone of its star and is estimated to have similar temperatures to Earth. We don’t know enough about the actual conditions on this planet yet either, however.

Fritz Benedict at McDonald Observatory, lead author of the new study. Image via McDonald Observatory.

With at least two planets now confirmed orbiting the closest star to our solar system, combined with the over 4,000 other exoplanets discovered so far, we now know that such exoworlds are common in our galaxy. That is a big step that brings us even closer to answering the biggest question of all: are we alone?

Bottom line: Astronomers at McDonald Observatory have confirmed a second planet orbiting the closest star to our sun.

Source: A Preliminary Mass for Proxima Centauri C

Via McDonald Observatory

from EarthSky https://ift.tt/2zlUV0O

Artist’s concept of Proxima Centauri b and c – depicted here as 2 black dots, a larger one and a smaller one – orbiting their red dwarf star. Proxima Centauri c, the larger planet, might also have a ring system. Image via Michele Diodati/ Medium.

Just a few days ago, scientists announced that the closest known Earth-sized exoplanet, Proxima Centauri b, had been confirmed to orbit the nearest star to our solar system. That’s an exciting development, but now, as scientists announced on June 2, 2020, it seems that another possible planet around the same star also has been verified … Proxima Centauri c! Both planets are only 4.2 light-years away.

The peer-reviewed results were published in Research Notes of the AAS back in April. Astronomer Fritz Benedict of McDonald Observatory presented the findings at the virtual 236th meeting of the American Astronomical Society.

Evidence for Proxima Centauri c was first announced earlier this year by a research group led by Mario Damasso of Italy’s National Institute for Astrophysics (INAF). But the evidence wasn’t conclusive. This second planet for Proxima is apparently a lot larger than Earth and orbits its star every 1,907 days. It orbits at about 1.5 times the distance from its star that Earth orbits from the sun. Not an extreme difference, but Proxima Centauri is a red dwarf star, smaller and cooler than our sun, so at that distance, the planet can be expected to be significantly colder than Earth.

Combined images from the SPHERE instrument on the Very Large Telescope (VLT) in Chile, which appear to show Proxima Centauri c as a bright dot. The location is right where the planet was predicted to be in its orbit. The star is hidden behind the black circle in the center. Image via Gratton et al./ A&A/ Nature Astronomy.

Even though Proxima Centauri is the closest star to the sun, it’s difficult to detect the planets orbiting it. Most exoplanets have been found via the transit method, and this system isn’t oriented with respect to Earth such that its planets transit in front of Proxima, from our perspective. So scientists have to use radial velocity observations, measurements of Proxima’s motion toward and away from Earth, to detect the tiny effects of the planets’ gravitational tuggings on the star.

Benedict’s idea was to look again at previous studies of the star from the 1990s from the Hubble Space Telescope (HST), which used the telescope’s Fine Guidance Sensors (FGS). The FGS can be used for astrometry, where scientists can take very accurate measurements of the positions and motions of objects in the sky. If Proxima Centauri c were really there, FGS should be able to detect it. Benedict said in a statement:

Basically, this is a story of how old data can be very useful when you get new information. It’s also a story of how hard it is to retire if you’re an astronomer, because this is fun stuff to do!

So what did Benedict and his team find?

When they looked at the old Hubble data, they found a planet with an orbital period of 1,907 days, which fit with what had been seen before, for the tentative Proxima Centauri c. The planet had been overlooked before because in the 1990s, researchers only checked the data for planets with orbital periods of less than 1,000 days.

Benedict combined the results of three studies: the Hubble/FGS astrometry, the radial velocity studies and images from the SPHERE instrument on the Very Large Telescope (VLT) in Chile, to better estimate the mass of Proxima Centauri c. He concluded that the planet is approximately seven times more massive than Earth.

Size comparison of the three stars in the Alpha Centauri system, including Proxima Centauri, and the sun. Image via PHL @ UPR Arecibo.

Proxima Centauri is the closest of the three stars in the Alpha Centauri system. Image via ESO/ BBC.

Earlier this year, scientists using the images from SPHERE found what appeared to be a large planet orbiting Proxima Centauri that coincided with the predicted position of Proxima Centauri c at the time.

But based on those images, it was found that Proxima Centauri c appeared to be brighter than expected. If the brightness was entirely from the light reflected off the planet itself, then the planet would be about five times larger than Jupiter. But since its estimated mass is more similar to Neptune’s, it may actually be smaller, but has dust clouds or a huge ring system around it. Determining whether it actually does or not will require more observations. It is bright enough that better images of it should be able to be taken by upcoming space telescopes. That’s not the case, unfortunately, with Proxima Centauri b, since it is smaller and much closer to the star. From another recent paper:

Proxima c could become a prime target for follow-up and characterization with next-generation direct imaging instrumentation due to the large maximum angular separation of ~1 arc second from the parent star. The candidate planet represents a challenge for the models of super-Earth formation and evolution.

As far as possible life is concerned, Proxima Centauri c may be too cold for life as we know it, but we just don’t know enough about it yet. Proxima Centauri b is a better candidate for being potentially habitable, since it is only slightly larger than Earth, orbits in the habitable zone of its star and is estimated to have similar temperatures to Earth. We don’t know enough about the actual conditions on this planet yet either, however.

Fritz Benedict at McDonald Observatory, lead author of the new study. Image via McDonald Observatory.

With at least two planets now confirmed orbiting the closest star to our solar system, combined with the over 4,000 other exoplanets discovered so far, we now know that such exoworlds are common in our galaxy. That is a big step that brings us even closer to answering the biggest question of all: are we alone?

Bottom line: Astronomers at McDonald Observatory have confirmed a second planet orbiting the closest star to our sun.

Source: A Preliminary Mass for Proxima Centauri C

Via McDonald Observatory

from EarthSky https://ift.tt/2zlUV0O