How small is the smallest habitable exoplanet?

The habitable zone as traditionally understood. New findings suggest that rocky planets smaller than Earth might still have liquid water, even if they’re somewhat outside a star’s primary habitable zone. Image via NASA/Astronomy Now.

What makes a planet potentially habitable? Life as we know it requires liquid water, among other factors. And it makes sense that larger rocky planets, like Earth, can maintain their liquid water – and their atmospheres – more easily than very small planets, whose gravity is weaker. But now, scientists from Harvard University have found that even very small rocky exoplanets, orbiting other stars, might still hold onto their water, boosting their chances for habitability. This finding expands on the traditional view of a star’s habitable zone, the zone around a star where temperatures are just right, allowing liquid water to exist.

The new peer-reviewed results were first published in The Astrophysical Journal on August 13, 2019.

If you don’t mind a bit of jargon, consider it this way. This new research redefines the lower limit in mass for potentially habitable exoplanets. Mass is simply the amount of matter a body contains. This new definition extends what we can think of as a habitable zone for small, low-mass and (because gravity depends on mass) low-gravity exoplanets.

How small is too small? The critical boundary point seems to be about 2.7 percent of the mass of Earth. Any planets less massive than that would lose their atmospheres to space before liquid water could form on their surfaces, and any water that might be present would vaporize or freeze. For comparison, the moon is 1.2 percent of Earth’s mass and Mercury is 5.53 percent.

As astronomer Constantin Arnscheidt, lead author of the paper, explained:

When people think about the inner and outer edges of the habitable zone, they tend to only think about it spatially, meaning how close the planet is to the star. But actually, there are many other variables to habitability, including [a planet’s] mass.

Setting a lower bound for habitability in terms of planet size gives us an important constraint in our ongoing hunt for habitable exoplanets and exomoons.

Robin Wordsworth, a co-author on the study, added:

Low-mass waterworlds are a fascinating possibility in the search for life, and this paper shows just how different their behavior is likely to be compared to that of Earth-like planets. Once observations for this class of objects become possible, it’s going to be exciting to try to test these predictions directly.

EarthSky 2020 lunar calendars are available! They make great gifts. Order now. Going fast!

Graphic depicting the new lower size limit for smaller rocky exoplanets. Very small planets – at least larger than only 2.7% of the mass of Earth – could maintain liquid water (depending on other factors), according to this new work, while planets smaller than that limit would have their water escape to space or freeze. Image via Harvard SEAS/Astrobiology Magazine.

According to traditional thinking about habitable zones, if a planet is too close to its star, a runaway greenhouse effect might occur, resulting in the planet losing all its water. This might happen even at the inner edge of a star’s habitable zone. Venus is often mentioned as an example of this process in our own solar system; it might once have had an ocean, but a runaway greenhouse effect occurred, leaving Venus dry as a bone and hot enough on its surface to melt lead.

According to its authors, the new study:

… sheds light on the important process of atmospheric evolution on small planets.

In other words, their work suggests that – for small exoplanets that are not too small – something interesting occurs as one of these planets, even if it is on the edge of its star’s habitable zone, begins to warm due to the greenhouse effect. In conditions of a warming atmosphere, on a low-mass world with relatively weak gravity the exoplanet’s atmosphere expands outward, becoming larger and larger relative to the size of the planet. This has the effect of increasing both the absorption and radiation of heat from the star, allowing the planet to achieve a kind of balance, maintaining a stable temperature. In this way, the atmospheric expansion might prevent small, low-gravity planets from experiencing a runaway greenhouse effect. Instead, they might be able to maintain their surface liquid water, even on the inner edge of the habitable zone, in relatively close proximity to their stars.

It’s also interesting to note that these findings, according to the researchers, appear to apply to both G-type sun-like stars as well as M-type red dwarf stars.

Smaller, cooler red dwarfs are the most common stars in our galaxy, so that in itself would increase the chances of finding more habitable worlds.

Jupiter’s icy ocean moon Europa as seen by Galileo in the late 1990s. The researchers wondered if these kinds of small icy moons could be habitable on the surface if they were closer to the sun, but the new study suggests they would be too small. Image via NASA/JPL-Caltech/SETI Institute/Europa Clipper.

The researchers also used their findings to figure out a question regarding certain moons in our solar system. Scientists had wondered if Jupiter’s icy moons Europa, Ganymede and Callisto could become habitable on the surface if they were closer to the sun, especially since they all have subsurface oceans beneath their ice crusts. The answer, though, seems to be no, as they are too small.

Although there is still a limit as to how small a planet can be and still be habitable, this new study shows that there could still be many more such worlds – smaller than Earth, but habitable, with liquid water – than previously thought. This bodes well in the search for life beyond our solar system.

Artist’s concept of one of the rocky worlds orbiting the TRAPPIST-1 red dwarf star, with possible liquid water on the surface. A new study says that smaller rocky planets could have a better chance of holding on to their water than previously thought. Image via ESO/M. Kornmesser.

Bottom line: A new study has found that small exoplanets have a better chance of holding on to their water than previously thought, increasing the chances that some of them could be habitable.

Source: Atmospheric Evolution on Low-gravity Waterworlds

Via Astrobiology Magazine

from EarthSky https://ift.tt/340PrSD

The habitable zone as traditionally understood. New findings suggest that rocky planets smaller than Earth might still have liquid water, even if they’re somewhat outside a star’s primary habitable zone. Image via NASA/Astronomy Now.

What makes a planet potentially habitable? Life as we know it requires liquid water, among other factors. And it makes sense that larger rocky planets, like Earth, can maintain their liquid water – and their atmospheres – more easily than very small planets, whose gravity is weaker. But now, scientists from Harvard University have found that even very small rocky exoplanets, orbiting other stars, might still hold onto their water, boosting their chances for habitability. This finding expands on the traditional view of a star’s habitable zone, the zone around a star where temperatures are just right, allowing liquid water to exist.

The new peer-reviewed results were first published in The Astrophysical Journal on August 13, 2019.

If you don’t mind a bit of jargon, consider it this way. This new research redefines the lower limit in mass for potentially habitable exoplanets. Mass is simply the amount of matter a body contains. This new definition extends what we can think of as a habitable zone for small, low-mass and (because gravity depends on mass) low-gravity exoplanets.

How small is too small? The critical boundary point seems to be about 2.7 percent of the mass of Earth. Any planets less massive than that would lose their atmospheres to space before liquid water could form on their surfaces, and any water that might be present would vaporize or freeze. For comparison, the moon is 1.2 percent of Earth’s mass and Mercury is 5.53 percent.

As astronomer Constantin Arnscheidt, lead author of the paper, explained:

When people think about the inner and outer edges of the habitable zone, they tend to only think about it spatially, meaning how close the planet is to the star. But actually, there are many other variables to habitability, including [a planet’s] mass.

Setting a lower bound for habitability in terms of planet size gives us an important constraint in our ongoing hunt for habitable exoplanets and exomoons.

Robin Wordsworth, a co-author on the study, added:

Low-mass waterworlds are a fascinating possibility in the search for life, and this paper shows just how different their behavior is likely to be compared to that of Earth-like planets. Once observations for this class of objects become possible, it’s going to be exciting to try to test these predictions directly.

EarthSky 2020 lunar calendars are available! They make great gifts. Order now. Going fast!

Graphic depicting the new lower size limit for smaller rocky exoplanets. Very small planets – at least larger than only 2.7% of the mass of Earth – could maintain liquid water (depending on other factors), according to this new work, while planets smaller than that limit would have their water escape to space or freeze. Image via Harvard SEAS/Astrobiology Magazine.

According to traditional thinking about habitable zones, if a planet is too close to its star, a runaway greenhouse effect might occur, resulting in the planet losing all its water. This might happen even at the inner edge of a star’s habitable zone. Venus is often mentioned as an example of this process in our own solar system; it might once have had an ocean, but a runaway greenhouse effect occurred, leaving Venus dry as a bone and hot enough on its surface to melt lead.

According to its authors, the new study:

… sheds light on the important process of atmospheric evolution on small planets.

In other words, their work suggests that – for small exoplanets that are not too small – something interesting occurs as one of these planets, even if it is on the edge of its star’s habitable zone, begins to warm due to the greenhouse effect. In conditions of a warming atmosphere, on a low-mass world with relatively weak gravity the exoplanet’s atmosphere expands outward, becoming larger and larger relative to the size of the planet. This has the effect of increasing both the absorption and radiation of heat from the star, allowing the planet to achieve a kind of balance, maintaining a stable temperature. In this way, the atmospheric expansion might prevent small, low-gravity planets from experiencing a runaway greenhouse effect. Instead, they might be able to maintain their surface liquid water, even on the inner edge of the habitable zone, in relatively close proximity to their stars.

It’s also interesting to note that these findings, according to the researchers, appear to apply to both G-type sun-like stars as well as M-type red dwarf stars.

Smaller, cooler red dwarfs are the most common stars in our galaxy, so that in itself would increase the chances of finding more habitable worlds.

Jupiter’s icy ocean moon Europa as seen by Galileo in the late 1990s. The researchers wondered if these kinds of small icy moons could be habitable on the surface if they were closer to the sun, but the new study suggests they would be too small. Image via NASA/JPL-Caltech/SETI Institute/Europa Clipper.

The researchers also used their findings to figure out a question regarding certain moons in our solar system. Scientists had wondered if Jupiter’s icy moons Europa, Ganymede and Callisto could become habitable on the surface if they were closer to the sun, especially since they all have subsurface oceans beneath their ice crusts. The answer, though, seems to be no, as they are too small.

Although there is still a limit as to how small a planet can be and still be habitable, this new study shows that there could still be many more such worlds – smaller than Earth, but habitable, with liquid water – than previously thought. This bodes well in the search for life beyond our solar system.

Artist’s concept of one of the rocky worlds orbiting the TRAPPIST-1 red dwarf star, with possible liquid water on the surface. A new study says that smaller rocky planets could have a better chance of holding on to their water than previously thought. Image via ESO/M. Kornmesser.

Bottom line: A new study has found that small exoplanets have a better chance of holding on to their water than previously thought, increasing the chances that some of them could be habitable.

Source: Atmospheric Evolution on Low-gravity Waterworlds

Via Astrobiology Magazine

from EarthSky https://ift.tt/340PrSD

Listen to the world’s loudest bird

Biologists report that they have recorded the loudest bird calls ever documented, made by male white bellbirds as part of their mating rituals in the mountains of the northern Amazon.

White bellbirds typically live in the high mountains of northern Brazil and southern Venezuela. The males are bright white with a striking black bill that has a wattle dangling from its top. Females have green plumage accented with streaks of brown.

Mario Cohn-Haft of the National Institute of Amazonian Research in Brazil, is co-author of the study, published October 21, 2019 in the peer-reviewed journal Current Biology. Cohn-Haft told the New York Times:

You can hear them from a mile away.

The white bellbirds have two song types, said the researchers. The first is relatively common and can reach around 116 decibels. (Normal human conversation, by way of comparison, clocks in at about 60 decibels.)The second song, which males emit when females are around, reached levels of around 125 decibels.

How loud is that? Standing beside a siren clocks in at 120 decibels. Biologist Jeff Podos at the University of Massachusetts, lead author of the study, said the songs are so deafening they reach decibel levels equal to the loudest human instruments, like the hammering of a pile driver.

Image via Anselmo d’Affonseca/Instituto Nacional de Pesquisas da Amazonia.

EarthSky’s 2020 lunar calendars are here! Get yours today. They make great gifts. Going fast.

The researchers note that it’s actually hard to describe how loud the bellbird’s call is, because it’s difficult to compare sounds from different distances. But the calls are so loud, they wonder how white bellbird females listen at close range without damaging their hearing. Podos said:

We were lucky enough to see females join males on their display perches. In these cases, we saw that the males sing only their loudest songs. Not only that, they swivel dramatically during these songs, so as to blast the song’s final note directly at the females. We would love to know why females willingly stay so close to males as they sing so loudly. Maybe they are trying to assess males up close, though at the risk of some damage to their hearing systems.

Image via Anselmo d’Affonseca.

For the research, the biologists used high-quality sound recorders plus special sound-level meters and high-speed video to slow the action enough for study.

The biologists aren’t sure how these birds can be so loud. Podos suggested that it might due to their wide beaks, which they use to swallow fruit whole. Other adaptations such as breathing musculature, head size, and the shape of the throat might influence the birds’ unusual aptitude as well. Podos said:

We don’t know how small animals manage to get so loud. We are truly at the early stages of understanding this biodiversity.

Bottom line: Listen to the song of the world’s loudest bird, the white bellbird.

Source: Extremely loud mating songs at close range in white bellbirds

Via University of Massachusetts

from EarthSky https://ift.tt/2olvjM0

Biologists report that they have recorded the loudest bird calls ever documented, made by male white bellbirds as part of their mating rituals in the mountains of the northern Amazon.

White bellbirds typically live in the high mountains of northern Brazil and southern Venezuela. The males are bright white with a striking black bill that has a wattle dangling from its top. Females have green plumage accented with streaks of brown.

Mario Cohn-Haft of the National Institute of Amazonian Research in Brazil, is co-author of the study, published October 21, 2019 in the peer-reviewed journal Current Biology. Cohn-Haft told the New York Times:

You can hear them from a mile away.

The white bellbirds have two song types, said the researchers. The first is relatively common and can reach around 116 decibels. (Normal human conversation, by way of comparison, clocks in at about 60 decibels.)The second song, which males emit when females are around, reached levels of around 125 decibels.

How loud is that? Standing beside a siren clocks in at 120 decibels. Biologist Jeff Podos at the University of Massachusetts, lead author of the study, said the songs are so deafening they reach decibel levels equal to the loudest human instruments, like the hammering of a pile driver.

Image via Anselmo d’Affonseca/Instituto Nacional de Pesquisas da Amazonia.

EarthSky’s 2020 lunar calendars are here! Get yours today. They make great gifts. Going fast.

The researchers note that it’s actually hard to describe how loud the bellbird’s call is, because it’s difficult to compare sounds from different distances. But the calls are so loud, they wonder how white bellbird females listen at close range without damaging their hearing. Podos said:

We were lucky enough to see females join males on their display perches. In these cases, we saw that the males sing only their loudest songs. Not only that, they swivel dramatically during these songs, so as to blast the song’s final note directly at the females. We would love to know why females willingly stay so close to males as they sing so loudly. Maybe they are trying to assess males up close, though at the risk of some damage to their hearing systems.

Image via Anselmo d’Affonseca.

For the research, the biologists used high-quality sound recorders plus special sound-level meters and high-speed video to slow the action enough for study.

The biologists aren’t sure how these birds can be so loud. Podos suggested that it might due to their wide beaks, which they use to swallow fruit whole. Other adaptations such as breathing musculature, head size, and the shape of the throat might influence the birds’ unusual aptitude as well. Podos said:

We don’t know how small animals manage to get so loud. We are truly at the early stages of understanding this biodiversity.

Bottom line: Listen to the song of the world’s loudest bird, the white bellbird.

Source: Extremely loud mating songs at close range in white bellbirds

Via University of Massachusetts

from EarthSky https://ift.tt/2olvjM0

Will you see all 5 bright planets?

By bright planet, we mean any solar system planet that is easily visible without an optical aid and that has been watched by our ancestors since time immemorial. In their outward order from the sun, the bright planets are Mercury, Venus, (Earth), Mars, Jupiter and Saturn. Mars is the only bright planet to appear in the morning sky, as shown on the above sky chart. The other four planets – Mercury, Venus, Jupiter and Saturn – come out after sunset.

Only two of these four evening planets readily show themselves in a dark sky: Jupiter and Saturn. These two worlds stay out till well after nightfall, making Jupiter and Saturn rather easy to spot in the evening sky.

Mercury and Venus demand a more diligent effort. That’s because Mercury and Venus sit low in the afterglow at sunset, and then follow the sun beneath the horizon shortly thereafter.

Venus and Mercury sit in the afterglow of sunset, and follow the sun beneath the horizon before it gets good and dark. Have binoculars handy!

In other words, you have to catch Mercury and Venus near the sunset point on the horizon at evening dusk. The Southern Hemisphere has the advantage over the Northern Hemisphere because these two worlds stay out longer after sundown at more southerly latitudes. Because Venus is the brightest planet and third-brightest celestial object overall (after the sun and moon), look for Venus first and then seek out Mercury with either the eye alone or binoculars. Dazzling Venus outshines fainter Mercury by about 40 times.

Here are the approximate setting times for Mercury and Venus at various latitudes (given an absolutely level horizon):

35 degrees north latitude
Mercury sets 55 minutes after sunset
Venus sets 55 minutes after sunset

Equator (0 degrees latitude)
Mercury sets 1 1/2 hours after sunset
Venus sets 1 1/4 hours after sunset

35 degrees south latitude
Mercury sets 2 hours after sunset
Venus sets 1 1/2 hours after sunset

Want more specific setting times? Click here for a recommended almanac.

Modesty-bright Mars may not be easy to spot in the morning sky, as it comes up only a short while before the break of day. You may need binoculars. This time around, though, it’s the Northern Hemisphere that has the advantage for catching Mars before sunrise. Here are the approximate rising times for Mars (presuming a level horizon):

35 degrees north latitude
Mars rises 1 1/2 hours before sunrise

Equator (0 degrees latitude)
Mars rises 1 1/10 hours before sunrise

35 degrees south latitude
Mars rises 1 hour before sunrise

Tomorrow – on October 26, 2019 – let the waning crescent moon serve as your guide to Mars. Click here to find out when the moon rises in your sky, remembering to check the moonrise and moonset box.

Watch for the young moon to join up with the planets Mercury and Venus in a few to several more days. The chart below is designed for mid-northern latitudes in the Northern Hemisphere. Once again, the Southern Hemisphere and northern tropics will enjoy a better view of the moon and evening planets.

Watch for the moon to swing by Venus and Mercury later this month.

For the ultimate challenge, try finding all five bright planets in the October 2019 night sky. Whereas Jupiter and Saturn adorn the evening sky, you have to catch Mercury and Venus shortly after sunset, and Mars shortly before sunrise. You may need binoculars to spot Venus and Mercury after sunset, and to catch Mars before sunrise.

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

By bright planet, we mean any solar system planet that is easily visible without an optical aid and that has been watched by our ancestors since time immemorial. In their outward order from the sun, the bright planets are Mercury, Venus, (Earth), Mars, Jupiter and Saturn. Mars is the only bright planet to appear in the morning sky, as shown on the above sky chart. The other four planets – Mercury, Venus, Jupiter and Saturn – come out after sunset.

Only two of these four evening planets readily show themselves in a dark sky: Jupiter and Saturn. These two worlds stay out till well after nightfall, making Jupiter and Saturn rather easy to spot in the evening sky.

Mercury and Venus demand a more diligent effort. That’s because Mercury and Venus sit low in the afterglow at sunset, and then follow the sun beneath the horizon shortly thereafter.

Venus and Mercury sit in the afterglow of sunset, and follow the sun beneath the horizon before it gets good and dark. Have binoculars handy!

In other words, you have to catch Mercury and Venus near the sunset point on the horizon at evening dusk. The Southern Hemisphere has the advantage over the Northern Hemisphere because these two worlds stay out longer after sundown at more southerly latitudes. Because Venus is the brightest planet and third-brightest celestial object overall (after the sun and moon), look for Venus first and then seek out Mercury with either the eye alone or binoculars. Dazzling Venus outshines fainter Mercury by about 40 times.

Here are the approximate setting times for Mercury and Venus at various latitudes (given an absolutely level horizon):

35 degrees north latitude
Mercury sets 55 minutes after sunset
Venus sets 55 minutes after sunset

Equator (0 degrees latitude)
Mercury sets 1 1/2 hours after sunset
Venus sets 1 1/4 hours after sunset

35 degrees south latitude
Mercury sets 2 hours after sunset
Venus sets 1 1/2 hours after sunset

Want more specific setting times? Click here for a recommended almanac.

Modesty-bright Mars may not be easy to spot in the morning sky, as it comes up only a short while before the break of day. You may need binoculars. This time around, though, it’s the Northern Hemisphere that has the advantage for catching Mars before sunrise. Here are the approximate rising times for Mars (presuming a level horizon):

35 degrees north latitude
Mars rises 1 1/2 hours before sunrise

Equator (0 degrees latitude)
Mars rises 1 1/10 hours before sunrise

35 degrees south latitude
Mars rises 1 hour before sunrise

Tomorrow – on October 26, 2019 – let the waning crescent moon serve as your guide to Mars. Click here to find out when the moon rises in your sky, remembering to check the moonrise and moonset box.

Watch for the young moon to join up with the planets Mercury and Venus in a few to several more days. The chart below is designed for mid-northern latitudes in the Northern Hemisphere. Once again, the Southern Hemisphere and northern tropics will enjoy a better view of the moon and evening planets.

Watch for the moon to swing by Venus and Mercury later this month.

For the ultimate challenge, try finding all five bright planets in the October 2019 night sky. Whereas Jupiter and Saturn adorn the evening sky, you have to catch Mercury and Venus shortly after sunset, and Mars shortly before sunrise. You may need binoculars to spot Venus and Mercury after sunset, and to catch Mars before sunrise.

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

What is a Venus node?

View larger. | Illustration of the orbits of Earth over a single year (2020) and of speedier Venus over 7 months. The planets, at the beginnings of the months, are exaggerated 300 times in size and the sun 5 times. Image via Guy Ottewell’s blog.

Originally published at Guy Ottewell’s blog. Reprinted here with permission.

Venus will be at the descending node of its orbit on Friday, October 25, 2019 at 02:00 UTC; translate UTC to your time. By American clocks, it’ll be four or more hours earlier, on October 24.

Ascending and descending nodes keep happening and may seem among the least exciting pf astronomical events, but they shape the orbits of the moving bodies and set them up for whatever else happens. And it happens that I’ve been working on a bit for my Venus book about that planet’s plane – its inclination and nodes – and have today fashioned the space diagram at the top of this post.

It shows the orbits of Earth in a year and of speedier Venus over seven months. The planets, at the beginnings of the months, are exaggerated 300 times in size and the sun five times.

Earth moves in the ecliptic plane; Venus does not. Its plane is at an inclination of 3.4 degrees to the ecliptic. In the diagram above, stalks connect the plane of Venus’ orbit to the ecliptic plane at intervals of five days. Also, Venus’s path is drawn with a thinner line when it is south of the ecliptic.

I chose the year 2020 because, in the 8-year Venus cycle, this is the type of year in which Venus’ inferior conjunction with the sun happens close to descending node. Inferior conjunction is the moment when Venus passes between us and the sun. Descending node is the moment when Venus slopes southward through the ecliptic plane. Ergo – at this upcoming inferior conjunction of Venus on June 3, 2020 – Venus very nearly passes in front of the sun, literally.

It did so eight and 16 years previously: the great transits of Venus. The cycle slowly evolves, and, in 2020, inferior conjunction will come just too soon – two days – before descending node. Note that – on the chart above – the red line for the conjunction points slightly above the sun; the blue line for the node points slightly to the right of the sun. Thus, in 2020, Venus will miss the sun on the northern side.

But the timing of the node passages determines much else. Because descending node is now, the next ascending node will be on February 15, 2020. That will cause Venus’s course next May to be seen by us far enough north that, as seen in our sky, the planet will cross the beautiful Pleiades star cluster and then reach its northernmost point in the whole cycle. And then it will seem to rush down rapidly to the descending node in our picture.

EarthSky 2020 lunar calendars are available! They make great gifts. Order now. Going fast!

So, back to Venus now, or, at least, Friday evening:

View larger. | Venus on the evening of Friday, October 25, 2019, via Guy Ottewell’s blog.

You can see that Venus is on the ecliptic. And is still almost down on the sunset horizon. But is inching out into the evening sky, and sharp observers are already monitoring it, or her.

At the ascending node in February, she will be only just past the First Point of Aries, which is the ascending node of the ecliptic on the equator.

Bottom line: A node is the intersection of one celestial body’s orbital plane with the plane of the ecliptic – that is, the plane created by Earth’s orbit around the sun – as projected onto the imaginary sphere of stars surrounding Earth. Venus will be at the descending node of its orbit on Friday, October 25, 2019 at 02:00 UTC; translate UTC to your time.

Read a definition of “node” from Encyclopedia Britannica

The definition of an orbital “node” from Wikipedia is more technical

Animation: Venus in late 2019 and early ’20

from EarthSky https://ift.tt/31JEJyn

View larger. | Illustration of the orbits of Earth over a single year (2020) and of speedier Venus over 7 months. The planets, at the beginnings of the months, are exaggerated 300 times in size and the sun 5 times. Image via Guy Ottewell’s blog.

Originally published at Guy Ottewell’s blog. Reprinted here with permission.

Venus will be at the descending node of its orbit on Friday, October 25, 2019 at 02:00 UTC; translate UTC to your time. By American clocks, it’ll be four or more hours earlier, on October 24.

Ascending and descending nodes keep happening and may seem among the least exciting pf astronomical events, but they shape the orbits of the moving bodies and set them up for whatever else happens. And it happens that I’ve been working on a bit for my Venus book about that planet’s plane – its inclination and nodes – and have today fashioned the space diagram at the top of this post.

It shows the orbits of Earth in a year and of speedier Venus over seven months. The planets, at the beginnings of the months, are exaggerated 300 times in size and the sun five times.

Earth moves in the ecliptic plane; Venus does not. Its plane is at an inclination of 3.4 degrees to the ecliptic. In the diagram above, stalks connect the plane of Venus’ orbit to the ecliptic plane at intervals of five days. Also, Venus’s path is drawn with a thinner line when it is south of the ecliptic.

I chose the year 2020 because, in the 8-year Venus cycle, this is the type of year in which Venus’ inferior conjunction with the sun happens close to descending node. Inferior conjunction is the moment when Venus passes between us and the sun. Descending node is the moment when Venus slopes southward through the ecliptic plane. Ergo – at this upcoming inferior conjunction of Venus on June 3, 2020 – Venus very nearly passes in front of the sun, literally.

It did so eight and 16 years previously: the great transits of Venus. The cycle slowly evolves, and, in 2020, inferior conjunction will come just too soon – two days – before descending node. Note that – on the chart above – the red line for the conjunction points slightly above the sun; the blue line for the node points slightly to the right of the sun. Thus, in 2020, Venus will miss the sun on the northern side.

But the timing of the node passages determines much else. Because descending node is now, the next ascending node will be on February 15, 2020. That will cause Venus’s course next May to be seen by us far enough north that, as seen in our sky, the planet will cross the beautiful Pleiades star cluster and then reach its northernmost point in the whole cycle. And then it will seem to rush down rapidly to the descending node in our picture.

EarthSky 2020 lunar calendars are available! They make great gifts. Order now. Going fast!

So, back to Venus now, or, at least, Friday evening:

View larger. | Venus on the evening of Friday, October 25, 2019, via Guy Ottewell’s blog.

You can see that Venus is on the ecliptic. And is still almost down on the sunset horizon. But is inching out into the evening sky, and sharp observers are already monitoring it, or her.

At the ascending node in February, she will be only just past the First Point of Aries, which is the ascending node of the ecliptic on the equator.

Bottom line: A node is the intersection of one celestial body’s orbital plane with the plane of the ecliptic – that is, the plane created by Earth’s orbit around the sun – as projected onto the imaginary sphere of stars surrounding Earth. Venus will be at the descending node of its orbit on Friday, October 25, 2019 at 02:00 UTC; translate UTC to your time.

Read a definition of “node” from Encyclopedia Britannica

The definition of an orbital “node” from Wikipedia is more technical

Animation: Venus in late 2019 and early ’20

from EarthSky https://ift.tt/31JEJyn

The psychology of thrills and chills

Monsters do not thrill psychologist Ken Carter, shown at Netherworld in Stone Mountain. Photo by Kay Hinton.

Psychologist Kenneth Carter is not a fan of Halloween haunted houses. But he has written a book about people who thrive on activities like entering dark passageways, sensing that something unknown and terrifying awaits around the next corner.

“I don’t enjoy having things come out of nowhere,” says Carter, whose long-anticipated book “Buzz! Inside the Minds of Thrill-Seekers, Daredevils and Adrenaline Junkies” comes out October 31. “Buzz!” both educates and entertains with insights from real-life adventurers, such as a scaler of skyscrapers, known as “Spider Man,” who enjoys hanging from great heights suspended by only his fingers.

Cambridge University Press is publishing the book, the culmination of years of research into high sensation-seeking people by Carter, a professor at Oxford College of Emory University and a self-described low sensation-seeking personality type.

“I love Halloween because it brings both extremes together, there’s something for everyone,” Carter says. “For me, it’s candy corn. That’s my second favorite candy, after Smarties. I enjoy the sweet, silly side of Halloween — not the dark, scary side. I don’t want to get lost in a corn maze or watch ‘The Children of the Corn.’”

Read the full story here.

from eScienceCommons https://ift.tt/2NaEIhD

Monsters do not thrill psychologist Ken Carter, shown at Netherworld in Stone Mountain. Photo by Kay Hinton.

Psychologist Kenneth Carter is not a fan of Halloween haunted houses. But he has written a book about people who thrive on activities like entering dark passageways, sensing that something unknown and terrifying awaits around the next corner.

“I don’t enjoy having things come out of nowhere,” says Carter, whose long-anticipated book “Buzz! Inside the Minds of Thrill-Seekers, Daredevils and Adrenaline Junkies” comes out October 31. “Buzz!” both educates and entertains with insights from real-life adventurers, such as a scaler of skyscrapers, known as “Spider Man,” who enjoys hanging from great heights suspended by only his fingers.

Cambridge University Press is publishing the book, the culmination of years of research into high sensation-seeking people by Carter, a professor at Oxford College of Emory University and a self-described low sensation-seeking personality type.

“I love Halloween because it brings both extremes together, there’s something for everyone,” Carter says. “For me, it’s candy corn. That’s my second favorite candy, after Smarties. I enjoy the sweet, silly side of Halloween — not the dark, scary side. I don’t want to get lost in a corn maze or watch ‘The Children of the Corn.’”

Read the full story here.

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When exoplanets collide

View larger. | Artist’s concept of a catastrophic collision between 2 rocky exoplanets in the planetary system BD +20 307. This system has been known for some years as a place where two worlds collided. In 2019, astronomers observed a change in the dust left behind by the collision. Image via NASA/SOFIA/Lynette Cook.

When astronomers speak of the process that formed our Earth, moon and the other worlds orbiting our sun, they often speak of collisions. The planets began as dust grains orbiting the newly born sun. The grains came together, making bigger grains, ultimately forming clumps that in turn collided with each other to form larger bodies known as planetesimals. More collisions … and more. And even after the planets we know today had ultimately formed, the collisions in our solar system did not stop. They peaked about 4 billion years ago during an interval called the Late Heavy Bombardment by astronomers. The heavily cratered surfaces on our moon, Mars and Mercury still retain scars from this period. Now – looking into our Milky Way galaxy – astronomers have obtained a dramatic glimpse of the aftermath of a collision between two planets in a distant solar system, 300 light-years away. What is it they are glimpsing? Not a collision itself, but the dust that was left behind from a collision that appears to have occurred in about the past 1,000 Earth-years.

The star system is known as BD +20 307. It consists of at least two stars that are at least a billion years old. That’s a fairly mature system; by contrast, our sun is 4.5 billion years old. Our sun and solar system retain some dust, too, mostly in the asteroid belt between Mars and Jupiter, or in the distant, cold Kuiper Belt beyond Neptune. But, by some estimates, the BD +20 307 system has a million times more dust than our solar system. Plus this dust debris isn’t cold, as would be expected in a solar system the age of BD +20 307. Instead, NASA said:

… the debris is warm, reinforcing that it was made relatively recently by the impact of two planet-sized bodies.

NASA’s Spitzer Space Telescope joined ground observatories in providing hints of this collision a decade ago, when the warm debris was first found. More recently, NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA) showed that – as viewed in the infrared – the brightness of the debris has increased by more than 10%.

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2009 artist’s concept of 2 planets colliding in the BD +20 307 system, via NuclearVacuum/ Wikimedia Commons.

It’s exciting when things in astronomy happen on timescales humans themselves experience. According to NASA, the increase in brightness is a sign there’s now even more warm dust in the BD +20 307 system than there was 10 years ago. NASA explained:

While there are several mechanisms that could cause the dust to glow more brightly – it could be absorbing more heat from the stars or moving closer to the stars – these are unlikely to happen in just 10 years, which is lightning fast for cosmic changes. A planetary collision, however, would easily inject a large amount of dust very quickly.

This provides more evidence that two exoplanets crashed into each other.

The astronomers who made the new observations with SOFIA published their results in the peer-reviewed Astrophysical Journal earlier this year. They said their results:

… further support that an extreme collision between rocky exoplanets may have occurred relatively recently. Collisions like these can change planetary systems. It is believed that a collision between a Mars-sized body and the Earth 4.5 billion years ago created debris that eventually formed Earth’s moon.

Maggie Thompson is an astrophysics PhD student at UC Santa Cruz and lead author on the paper about warmer dust in the BD +20 307 system. Image via Thompson’s website.

The paper’s lead author Maggie Thompson commented:

The warm dust around BD +20 307 gives us a glimpse into what catastrophic impacts between rocky exoplanets might be like. We want to know how this system subsequently evolves after the extreme impact.

Alycia Weinberger is an observational astronomer interested in planet formation, exoplanets and brown dwarfs. She’s lead investigator on the project to study the BD +20 307 system. Image via Carnegie Institution for Science.

Alycia Weinberger is a staff scientist at the Carnegie Institution for Science’s Department of Terrestrial Magnetism in Washington and lead investigator on the project to study the BD +20 307 system. She said:

This is a rare opportunity to study catastrophic collisions occurring late in a planetary system’s history. The SOFIA observations show changes in the dusty disk on a timescale of only a few years.

The team is analyzing data from follow-up observations to see if there are further changes in the system.

This artist’s concept of a collision in the BD +20 307 system comes from 2005. In that year, observations from the Gemini/Keck observatories in Hawaii revealed dust and caused astronomers to begin speculating about a collision between worlds. They said at that time collisions responsible for the dust could range in size from asteroids (approximated here) to planets the size of the Earth or Mars. Image via Gemini Observatory/Jon Lomberg/Space.com.

Bottom line: Astronomers using SOFIA see 10% more warm dust in the double star system known as BD +20 307 than they did 10 years ago. This fast increase in the amount of warm dust in the system supports the idea that astronomers are witnessing the aftermath of a collision between worlds.

Source: Studying the Evolution of Warm Dust Encircling BD +20 307 Using SOFIA

Via NASA

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

View larger. | Artist’s concept of a catastrophic collision between 2 rocky exoplanets in the planetary system BD +20 307. This system has been known for some years as a place where two worlds collided. In 2019, astronomers observed a change in the dust left behind by the collision. Image via NASA/SOFIA/Lynette Cook.

When astronomers speak of the process that formed our Earth, moon and the other worlds orbiting our sun, they often speak of collisions. The planets began as dust grains orbiting the newly born sun. The grains came together, making bigger grains, ultimately forming clumps that in turn collided with each other to form larger bodies known as planetesimals. More collisions … and more. And even after the planets we know today had ultimately formed, the collisions in our solar system did not stop. They peaked about 4 billion years ago during an interval called the Late Heavy Bombardment by astronomers. The heavily cratered surfaces on our moon, Mars and Mercury still retain scars from this period. Now – looking into our Milky Way galaxy – astronomers have obtained a dramatic glimpse of the aftermath of a collision between two planets in a distant solar system, 300 light-years away. What is it they are glimpsing? Not a collision itself, but the dust that was left behind from a collision that appears to have occurred in about the past 1,000 Earth-years.

The star system is known as BD +20 307. It consists of at least two stars that are at least a billion years old. That’s a fairly mature system; by contrast, our sun is 4.5 billion years old. Our sun and solar system retain some dust, too, mostly in the asteroid belt between Mars and Jupiter, or in the distant, cold Kuiper Belt beyond Neptune. But, by some estimates, the BD +20 307 system has a million times more dust than our solar system. Plus this dust debris isn’t cold, as would be expected in a solar system the age of BD +20 307. Instead, NASA said:

… the debris is warm, reinforcing that it was made relatively recently by the impact of two planet-sized bodies.

NASA’s Spitzer Space Telescope joined ground observatories in providing hints of this collision a decade ago, when the warm debris was first found. More recently, NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA) showed that – as viewed in the infrared – the brightness of the debris has increased by more than 10%.

EarthSky 2020 lunar calendars are available! They make great gifts. Order now. Going fast!

2009 artist’s concept of 2 planets colliding in the BD +20 307 system, via NuclearVacuum/ Wikimedia Commons.

It’s exciting when things in astronomy happen on timescales humans themselves experience. According to NASA, the increase in brightness is a sign there’s now even more warm dust in the BD +20 307 system than there was 10 years ago. NASA explained:

While there are several mechanisms that could cause the dust to glow more brightly – it could be absorbing more heat from the stars or moving closer to the stars – these are unlikely to happen in just 10 years, which is lightning fast for cosmic changes. A planetary collision, however, would easily inject a large amount of dust very quickly.

This provides more evidence that two exoplanets crashed into each other.

The astronomers who made the new observations with SOFIA published their results in the peer-reviewed Astrophysical Journal earlier this year. They said their results:

… further support that an extreme collision between rocky exoplanets may have occurred relatively recently. Collisions like these can change planetary systems. It is believed that a collision between a Mars-sized body and the Earth 4.5 billion years ago created debris that eventually formed Earth’s moon.

Maggie Thompson is an astrophysics PhD student at UC Santa Cruz and lead author on the paper about warmer dust in the BD +20 307 system. Image via Thompson’s website.

The paper’s lead author Maggie Thompson commented:

The warm dust around BD +20 307 gives us a glimpse into what catastrophic impacts between rocky exoplanets might be like. We want to know how this system subsequently evolves after the extreme impact.

Alycia Weinberger is an observational astronomer interested in planet formation, exoplanets and brown dwarfs. She’s lead investigator on the project to study the BD +20 307 system. Image via Carnegie Institution for Science.

Alycia Weinberger is a staff scientist at the Carnegie Institution for Science’s Department of Terrestrial Magnetism in Washington and lead investigator on the project to study the BD +20 307 system. She said:

This is a rare opportunity to study catastrophic collisions occurring late in a planetary system’s history. The SOFIA observations show changes in the dusty disk on a timescale of only a few years.

The team is analyzing data from follow-up observations to see if there are further changes in the system.

This artist’s concept of a collision in the BD +20 307 system comes from 2005. In that year, observations from the Gemini/Keck observatories in Hawaii revealed dust and caused astronomers to begin speculating about a collision between worlds. They said at that time collisions responsible for the dust could range in size from asteroids (approximated here) to planets the size of the Earth or Mars. Image via Gemini Observatory/Jon Lomberg/Space.com.

Bottom line: Astronomers using SOFIA see 10% more warm dust in the double star system known as BD +20 307 than they did 10 years ago. This fast increase in the amount of warm dust in the system supports the idea that astronomers are witnessing the aftermath of a collision between worlds.

Source: Studying the Evolution of Warm Dust Encircling BD +20 307 Using SOFIA

Via NASA

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

NOAA’s US winter weather outlook

On October 17, 2019, NOAA issued its annual winter outlook for temperature, precipitation and drought. According to NOAA’s Climate Prediction Center, winter temperatures in 2019-2020 are likely to be above average in most of the western, southern and eastern U.S., as well as in Alaska and Hawaii.

While El Niño often influences the winter, NOAA scientists say that neutral conditions are in place this year and are expected to persist into the spring. Mike Halpert, deputy director of NOAA’s Climate Prediction Center, said in a statement:

Without either El Niño or La Nina conditions, short-term climate patterns like the Arctic Oscillation will drive winter weather and could result in large swings in temperature and precipitation.

The Arctic Oscillation (AO) is an atmospheric circulation pattern over the mid-to-high latitudes of the Northern Hemisphere that influences the number of arctic air masses that move into the U.S.

If you’re not too sure about El Niño, check out the video below, which describes El Niño and its cooler cousin, La Niña, as opposite phases of what is known as the El Niño-Southern Oscillation. They are complex, naturally occurring climatic phenomena, occurring at irregular intervals of between two and seven years.

Here are some of the key points from NOAA’s 2019-20 U.S. winter outlook:

– The greatest likelihood for warmer-than-normal conditions are in Alaska and Hawaii, with more modest probabilities for above-average temperatures spanning large parts of the remaining lower 48 from the West across the South and up the eastern seaboard.

– The Northern Plains, Upper Mississippi Valley, and the western Great Lakes have equal chances for below-, near- or above-average temperatures.

– No part of the U.S. is favored to have below-average temperatures this winter.

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This 2019-20 Winter Outlook map for temperature shows warmer-than-average temperatures are likely for much of the U.S. this winter. Image via NOAA.

– Wetter-than-average conditions are most likely in Alaska and Hawaii this winter, along with portions of the Northern Plains, Upper Mississippi Valley, the Great Lakes and parts of the Mid-Atlantic and Northeast.

– Drier-than-average conditions are most likely for Louisiana, parts of Texas, Mississippi, Arkansas and Oklahoma as well areas of northern and central California.

= The remainder of the U.S. falls into the category of equal chances for below-, near-, or above-average precipitation.

This 2019-20 Winter Outlook map for precipitation shows wetter-than-average weather is most likely across the Northern Tier of the U.S. this coming winter. Image via NOAA.

Photo via Peter Montanti/Mountain Photographics.

Bottom line: NOAA issued its 2019-2020 winter weather outlook report.

Read more from NOAA

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

On October 17, 2019, NOAA issued its annual winter outlook for temperature, precipitation and drought. According to NOAA’s Climate Prediction Center, winter temperatures in 2019-2020 are likely to be above average in most of the western, southern and eastern U.S., as well as in Alaska and Hawaii.

While El Niño often influences the winter, NOAA scientists say that neutral conditions are in place this year and are expected to persist into the spring. Mike Halpert, deputy director of NOAA’s Climate Prediction Center, said in a statement:

Without either El Niño or La Nina conditions, short-term climate patterns like the Arctic Oscillation will drive winter weather and could result in large swings in temperature and precipitation.

The Arctic Oscillation (AO) is an atmospheric circulation pattern over the mid-to-high latitudes of the Northern Hemisphere that influences the number of arctic air masses that move into the U.S.

If you’re not too sure about El Niño, check out the video below, which describes El Niño and its cooler cousin, La Niña, as opposite phases of what is known as the El Niño-Southern Oscillation. They are complex, naturally occurring climatic phenomena, occurring at irregular intervals of between two and seven years.

Here are some of the key points from NOAA’s 2019-20 U.S. winter outlook:

– The greatest likelihood for warmer-than-normal conditions are in Alaska and Hawaii, with more modest probabilities for above-average temperatures spanning large parts of the remaining lower 48 from the West across the South and up the eastern seaboard.

– The Northern Plains, Upper Mississippi Valley, and the western Great Lakes have equal chances for below-, near- or above-average temperatures.

– No part of the U.S. is favored to have below-average temperatures this winter.

EarthSky 2020 lunar calendars are available! They make great gifts. Order now. Going fast!

This 2019-20 Winter Outlook map for temperature shows warmer-than-average temperatures are likely for much of the U.S. this winter. Image via NOAA.

– Wetter-than-average conditions are most likely in Alaska and Hawaii this winter, along with portions of the Northern Plains, Upper Mississippi Valley, the Great Lakes and parts of the Mid-Atlantic and Northeast.

– Drier-than-average conditions are most likely for Louisiana, parts of Texas, Mississippi, Arkansas and Oklahoma as well areas of northern and central California.

= The remainder of the U.S. falls into the category of equal chances for below-, near-, or above-average precipitation.

This 2019-20 Winter Outlook map for precipitation shows wetter-than-average weather is most likely across the Northern Tier of the U.S. this coming winter. Image via NOAA.

Photo via Peter Montanti/Mountain Photographics.

Bottom line: NOAA issued its 2019-2020 winter weather outlook report.

Read more from NOAA

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