Atmosphere detected on GJ 3470b

[Jason]

Distant Exoplanet Has Blue Skies
Not all planets have a blue sky. Mars, for example, with its much thinner atmosphere has more of a brown sky. Rayleigh scattering is a subtle effect, so it’s been difficult to observe beyond our solar system. But recently a team has observed Rayleigh scattering in the atmosphere of a planet about 100 light years away.

(...)

But if we can only observe the planet by its effect on starlight, how do we know there is Rayleigh scattering in its atmosphere?

To do this the team used a rather ingenious technique. They analyzed the brightness dip of the star during a transit at different wavelengths, and found that the calculated size of the planet increased at shorter wavelengths.

https://briankoberlein.com/2015/12/04/d ... lue-skies/

[mistermack]

Sounds like a hellish world.

Atmosphere on a planet isn't a shock discovery. Venus has an atmosphere on steroids compared to Earth.
The atmosphere at ground level is so thick, and the pressure is so high, it's like being under the ocean on Earth.

This planet that they've studied seems to be an odd one. It's about the size of Neptune, which is three times the diameter of Earth, and about fifteen times as massive. But they say that it's year is just three Earth days long, so it must be very close to it's star. Neptune's year is about 150 Earth years.

Mercury and Venus have orbits of about 90 days and 250 days. And they are scorched by the Sun. So imagine how close to it's star this one is, to orbit in 3 days. And imagine how scorched it must be.

I'm surprised that they say it's atmosphere would be mostly Hydrogen and Helium. You would think that the Solar wind would have blasted it away. Maybe it's greater gravity holds it in.

It must be a hell-hole though.

[JimC]

Sounds like a hellish world.

Atmosphere on a planet isn't a shock discovery. Venus has an atmosphere on steroids compared to Earth.
The atmosphere at ground level is so thick, and the pressure is so high, it's like being under the ocean on Earth.

This planet that they've studied seems to be an odd one. It's about the size of Neptune, which is three times the diameter of Earth, and about fifteen times as massive. But they say that it's year is just three Earth days long, so it must be very close to it's star. Neptune's year is about 150 Earth years.

Mercury and Venus have orbits of about 90 days and 250 days. And they are scorched by the Sun. So imagine how close to it's star this one is, to orbit in 3 days. And imagine how scorched it must be.

I'm surprised that they say it's atmosphere would be mostly Hydrogen and Helium. You would think that the Solar wind would have blasted it away. Maybe it's greater gravity holds it in.

It must be a hell-hole though.

There may also be continuing out-gassing from the interior replacing the loss via a solar wind...

[Jason]

Atmosphere on another planet isn't remarkable, but the method they used to detect it on an extrasolar planet struck me as clever.

[mistermack]

Atmosphere on another planet isn't remarkable, but the method they used to detect it on an extrasolar planet struck me as clever.

Me too. Although I'm not sure about the conclusion that the atmosphere is likely hydrogen and helium.
From the way it reads, that might be the writer of the article who thought that, just because the planet is the same size as Neptune, which has an atmosphere of hydrogen and helium.

We have an atmosphere of mainly nitrogen, and our sky is blue, so the main gas could be nitrogen, or any smaller molecule, that scatters mostly blue light.

If the atmosphere is of hydrogen and helium, it could be constant outgassing, as Jim said, or it could be that the planet has a very strong magnetic field, which deflects the solar wind, a bit like ours does, on Earth.

[JimC]

Good point about the magnetic field, mm, although it would probably need to be a fair bit stronger than Earth's, given the proximity of the planet to its star...