# Super-Earth orbiting red dwarf

Astronomers have discovered the most Earth-like exoplanet yet. The world, which orbits a red dwarf star, is about five times as massive as Earth, and thanks to its position, should be capable of holding liquid water. The researchers made the discovery using the 3.6 metre telescope at the European Southern Observatory in Chile …

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#### Well maybe

I note that the temperature estimates are based on (presumably reasonable) guesses about the albedo of the planet, which they've assumed lies somewhere between the albedo of Venus (very high) to the albedo of Earth (moderate). If the planetary body is of a very low albedo (which it could be if there's a lot of vulcanism or atmospheric pollution), then the temperature estimate could be wildly innacurate, and liquid water may not be possible.

Wonder what the g-field would be?

#### Gravitational force

Rough calculations, but apparently the radius is 1.5 times that of the Earth, mass is 5 times that of the Earth. Given that, the gravitational pull at the surface should be 2.2 times that of the Earth, about 21.8m/s/s.

Indigenous Hobbits anyone? I think we should rename it Middle Earth instead of Super Earth.

#### And there's Krypton!

Sounds like Kal-el's homeworld has been discovered, before its sun exploded (in light-time, at least). So close on the heels of the discovery of Kryptonite, too.

You can see another Boffin-picture at the NASA pix site for today:

http://antwrp.gsfc.nasa.gov/apod/astropix.html

If you read this after 20070426, you'll have to check the archives.

#### My rough-and-ready calculations...

make it about 2.2 time Earth's gravity.

Which should be checked by someone who knows what they're talking about.

#### How bright would daylight be?

How bright would daylight be? The star is dimmer than our sun, but the planet is closer to it's star than we are to our sun... so maybe its daylight could be similar to ours???

#### Take-away anyone?

I read another article that claimed the star is 20 light years distant from Earth.

That's 20 years travelling at the spped of light.

Methinks my chicken vindaloo might be a tad cold by the time it arrives from my favourite Earth curry house. In fact, it may have had time to evolve into a higher life form.

#### Higher form of life

What, u mean a balti chicken tikka bhuna with pilau rice and a peshwari naan?

#### What it might be like there

So we finally found an Earthlike planet... I can see the history books of that planet's civilisation now (H.G. Wells Analogy #1):

"No one would have believed, in the last years of the final century, that Gliesian affairs were being watched keenly and closely by intelligences greater than Gliesian's and yet as mortal as their own..."

Ok, enough of the Schadenfreude... let's do some astronomy! We have a planet of about 5 EM at about 1.5 ER, which gives a surface gravity of 21.6 ms^2 or, as others have posted, about 2.2 g. Phew - I weigh 80 kg here on Earth, I'd weigh 176 kg on that planet. (H.G. Wells Analogy #2: We'd have the same gravitational problems that confronted the Martians upon their invasion of Earth!) I wouldn't want to wrestle with the natives... if, indeed there are any...

The planet orbits its primary in 13 days, in a very close orbit. There is a Neptune sized gas giant in an even closer orbit (if we go by the orbit/distance ratios of our own solar system, this would give it a sidereal period of about 8 days.) There's another one that takes 84 days to complete an orbit.

The inner planet would almost certainly perturb the orbit of our Earthlike one, most probably giving it a highly elliptical orbit with a high rate of precession of the perihelion. This means that the planet's solar year would be significantly longer than its sidereal year, perhaps even as much as a day. Temperature variations between perihelion and aphelion would therefore be extreme, mitigated only by the rapid velocity of the orbit. You'd have a week of global summer, followed by a week of global winter.

In such a close orbit, the odds are high that the planet is also subject to synchronous rotation; that is, orbiting with one hemisphere permanently facing the sun, the other in permanent darkness - much like the Moon in relation to the Earth. If the planet also has a significant obliquity of its ecliptic (or axial inclination to the old school) this would cause the sun to rise and set only around the polar regions during the planet's year. The sun would not traverse the sky, but would rise a short way above the horizon for 6.5 days, reverse, set in the same place it rose, and remain below the horizon for 6.5 days. The size of this polar region would of course be determined by the degree of obliquity.

This means that liquid water (and hence life) could only exist around the polar regions, and in a narrow band around the day/night terminator. Libration due to orbital precession could extend the width of the terminator band quite significantly; but most of the hemisphere facing the sun would be too hot, and the hemisphere in darkness would be frozen solid.

This would set up massive convection in the atmosphere. Superheated gas rising in the middle of the sunward hemisphere would flow in high-altitude currents toward the dark side, carrying water vapour continuously into the frozen zone and depositing it there. Cold, dry air from the frozen zone would then flow sunward at the surface, picking up water vapour from any open water in the polar and terminator belts, and carrying it into the hot zone. Eventually, all of the planet's exposed water would be deposited as a permanent ice cap on the dark side, possibly leaving the rest of the planet as a dessicated desert.

However, libration would periodically expose parts of the ice cap to sunlight, which could melt the ice and continue the process indefinitely. In this scenario, we thus have a continuous cycle of freezing, thawing and evaporation occurring in a double hourglass-shaped "life zone" with the bulges at the poles connected by a narrow strip along the day/night terminator. It would be in this region that life, if any, could evolve.

I fed this information into Celestia and came up with some more interesting data: the sun would appear to subtend 2.5 degrees of arc, or nearly 5 times as big as the Sun as seen from Earth. Transits of the inner planet would appear as miniature annular eclipses easily visible to the naked eye; the inner planet itself would show a visible disc, at its closest (inferior conjunction) it would appear almost as big as the Moon as seen from Earth (or even bigger, depending on the orbital eccentricity!)

However, the amount of UV radiation would be small, as these stars radiate mostly in the visible and infra-red. The light would be very red by human standards, even where the sun was high in the sky. Imagine the colour and brightness of sunset at noon. Assuming that life is present, producing free oxygen in the atmosphere, the sky would be greenish rather than blue because of this aspect of the star's spectrum.

So despite the star's large apparent diameter, the level of light reaching the surface would be rather less that that of Earth, and shadows would be much more diffuse due to the size of the light source. Any plant life would most likely be "one-sided", with all their leaves facing the direction the sunlight is permanently coming from, and presumably some protective structure on the other side to resist the freezing wind that would be blowing continuously from the night side. Any animal life would have to live in shelter from that same wind; they would probably live in the lee of the plants, or in burrows facing the sunlight, to obtain as much warmth as possible.

All in all, we have a world that, while it could theoretically support life of its own, would have conditions so alien that Earth life could not survive there. Even if life exists on that planet, its conditions would thus be inimical to Earth life - just as our world would be inimical to that planet's life. So we have H.G Wells Analogy #3:

"By the toll of a billion deaths, man has bought his birthright of the earth, and it is his against all comers; it would still be his were the Martians ten times as mighty as they are. For neither do men live nor die in vain."

And the same holds true for the Gliesians.

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