## Super-Earth Discovered In Star's Habitable Zone 135 135

astroengine writes

*"The family of planets circling a relatively close dwarf star has grown to six, including a potential rocky world at least seven times more massive than Earth that is properly located for liquid water to exist on its surface, a condition believed to be necessary for life. Scientists added three new planets to three discovered in 2008 orbiting an orange star called HD 40307, which is roughly three-quarters as massive as the sun and located about 42 light-years away in the constellation Pictor. Of particular interest is the outermost planet, which is believed to fly around its parent star over 320 days, a distance that places it within HD 40307's so-called "habitable zone.""*
## Re:Fermi's p (Score:5, Informative)

Depends on the diameter and the rate of rotation.

## Re:Apostrophe! (Score:3, Informative)

Star's, not stars', unless the planet is orbiting more than one star at a time. Didn't we just talk about apostrophe abuse in another Slashdot headline a couple days ago?

No, I'm pretty sure it was Child Abuse.

## Re:Fermi's p (Score:5, Informative)

seven times more massive than Earth...so much for their early space program

Assuming 2 planets have equal densities, Mass increases proportional to R^3, but gravity is proportional to the inverse squared of the distance.... As a result, surface gravity increases only linearly with the radius.... in this case, the planet would have 1.9 times the radius of the Earth if it's the same density.

Earth has a very high density actually at 5.5g/cm3, it's actually the densest planetary object in our solar system. Most terrestrial objects are closer to 2 and the larger ones tend to be 3. It is entirely possible that it'll have a comparable surface gravity.

## Re:Direct imaging!? (Score:5, Informative)

Taking pictures of bodies like Pluto isn't hard because it's far away from us, it's hard because it's far away from a light source and receives 1/2000th the illumination of the Earth, being small and far doesn't help, but that's not our big problem. Given that it's in the habitable zone, the amount of light should be comparable to that of the Earth, not something and given the expected surface area is nearly 4 times larger than that of the Earth's, it should be a quite bright pixel.

## Re:Fermi's p (Score:5, Informative)

No, his math is quite correct: M=d*4*pi*r^3, so M(p)/M(e) = (d*4*pi*r(p)^3)/(d*4*pi*r(e)) which simplifies to r(p)^3/r(e)^3, or (r(p)/r(e))^3, thus the ratio is the cube-root of 7: 1.913 (or 7.1: 1.922). Still, 2G would be a cow for us.

## Re:Fermi's p (Score:5, Informative)

Solids and liquids are not significantly compressible.

While you're correct that they're a lot less compressible than a gas, you most certainly can still compress solids and liquids if you press hard enough. There's a lot of pressure inside the core of a planet...

## Re:Fermi's p (Score:5, Informative)

Your math is a little off. If the density were the same as Earth's, the diameter would be proportional to the cube root of the mass ratios, or slightly less than 2 times that of Earth. The surface gravity is proportional to mass (7x) and inversely so to the square of the radius (~1/4) so 7/4 is about 1.75 surface gravity compared to Earth. If there were a comparable 'day' length, then the velocity at the equator would be about 2x that of Earth. An extra 1000 mph liftoff boost vs 1.75 local g, not so hard to overcome.

And since we know nothing about the planet other than the mass, this is all silly speculation.