Smallest earth-like planet to date

[ianmacfarlane]

Smallest earth-like planet to date

The newly discovered planet weighs about five Earth masses and is located 30 light-years from Earth. A planet of this mass is expected to be rocky rather than gaseous

That mass means the planet is a "super-Earth," a category that includes planets with masses of between one and 10 times the Earth. Astronomers estimate its radius to be about 50 percent greater than that of Earth's radius of 4,000 miles (6,400 kilometers).

Dubbed GJ 436c, the planet orbits its host star (GJ 436) in just 5.2 Earth days, and is thought to complete a revolution about its axis in 4.2 Earth days. A complete revolution of Earth takes 24 hours and a full orbit around the sun takes 365 days.

[ajtribick]

Calling it the "smallest exoplanet yet" is misleading: why don't the pulsar planets count?

I like the way this article seems to make no distinction between quantities which have been measured and those which are estimated purely on theoretical considerations, e.g. the reason why the rotation period is "thought to be" 4.2 days. They don't mention the fact that the radius has to be estimated from theoretical considerations rather than actual measurements of the planet's size, hiding behind the phrase "Astronomers estimate its radius to be..."

As for calling it "Earth-like", I calculate that the equilibrium temperature is going to be somewhere around 300 degrees C, and it is not even clear whether it would be rocky rather than an icy planet that has migrated inwards (perhaps like the neighbouring "hot Neptune" GJ 436b).

The relevant paper is up at arXiv, and the planet is currently listed as "unconfirmed" on the Extrasolar Planets Enyclopaedia.

[symaski62]

http://www.ucl.ac.uk/media/library/exoplanet

[eburacum45]

“Calculations indicate that the temperature of the planet could be within 400-700 Kelvin [127-427 Celsius], but it could locally be as low as 350 K [77 C] at the poles, depending on the type of atmosphere.”
Another quite hot superterrestrial, then. A class of planet I'd not really considered much before, but such planets seem to be in the news quite a lot recently.

[ajtribick]

The discovery has been retracted