I've been told by someone at NSF that there may be an announcement today of an extrasolar "earth-like" planet (in terms of mass) at 1 PM. We'll keep an eye out.

[Update at 11:30 AM EDT]

Here's a link to a webcast on it, coming up in an hour and a half. The person who notified me of this writes:

"I believe, based on the level of media they're expecting that it will be an earth-size and mass planet outside of the solar system.

Let's keep our fingers crossed."

[Update at 2 PM]

OK, it's "more earth like than anything previously found," but still not that earth like. It masses several times as much as the earth, at a distance of only a couple million miles from its star, with a year of only two earth days. Sounds more like a large "Mercury-like" planet.

Not to complain but where is the link?

Whiner...

It's up there now, sorry 'bout that.

This'll be interesting...not just for the size of the planet itself but for the type of star it's associated with and orbital distance. The size of Earth and its just-right distance from the sun may be a random result of chaotic planet formation, but the existence of Venus makes me wonder if there's more to it. That is, there are two nearly identical (in size) planets next to each other. Instead of Earth being a fluke, maybe there are physical factors that encourage the formation of Earth-sized planets within a certain region at a certain distance from Sun-like stars? While Venus also demonstrates that not every Earth-sized planet is going to be Eden II, the possibility that most Sun-like stars would have one or two Earth-sized planets at about the right distance would certainly make the overall odds go up for life-bearing worlds.

--Dwight

Gliese 876 is a red dwarf, about 15 LY away -- this planet is 7.5 E-mass, in period of 2 days --
temp 400 to 700 deg F, but massive enough to retain substantial atmosphere. Prob tidally locked.

Where is Frank Herbert when we really need him?

Very cool, in all events, because it means they're getting better at finding smaller masses. My guess, of course, is that it's just so much easier to find something that goes from minimum to max freq. shift in 12 hours. More patience would be required to find a terrestrial planet around, say, Delta Pavonis, since that would be a 400 day orbit, or a 100 day period between the top and bottom of the curve.

I think Arrakis was supposed to be around Canopus, IIRC.

The planet described sounds like a tidally locked boiling freezing hell hole. Mercury would be "Tahiti-like" compared to this place.

"Earth-like" makes for a much better press release than "Mercury-like."

It's much easier to find these planets in close orbits. The velocity of the star goes as one over the square root of the orbital radius, or one over the cube root of the period. A period of 2 days gives a doppler shift more than five times larger than a period of one year.

The 'hot Jupiters' were very detectable by the doppler method, with signals many times larger than the velocity error bars. It's not surprising a hefty rocky planet would also be detectable in a close orbit.

I suspect this world would have a pretty hefty atmosphere. The escape velocity is roughly twice earth's, so even a hot exosphere wouldn't allow CO2 to escape. This would prevent the day/night sides from being too different in temperature.

I don't know how they define "Earth-like" but one definition I heard what that the planet or moon had to have 0.5 to 5 Earth-masses and reside in a region (by stellar output) where liquid water could exist. Venus barely qualifies as "Earth-like" (it's too close to the Sun). Mars is almost too far away and it's too light at a tenth of an Earth-mass.

Note the special circumstances that enabled detection of a planet this small with the present technology. The fact that the two big planets in the system are in resonance with each other acted as a sort of 'lever arm'. The Doppler shift should follow a very specific pattern, such that fairly small deviations from that pattern become detectable. In essence, part of the detection would be coming from direct tugging on the star, and part due to the influence of the smaller world on the more massive world next farther out. This world is a half-Uranus mass and my guess is that, even given the star's lower mass, this would be an out-of-reach detection right now in almost any other planetary system.

- Eric.

Actually, the third planet would have been detectable even without the two large ones there. What the two large planets did was (1) provide a justification for using the Keck on this particular star over a period of years, and (2) enable (through modeling of their affect on each other) the astronomers to determine those planets' absolute masses, and therefore the inclination of the orbital plane of the star system to the line of sight. This enabled them to closely estimate the mass of the third planet, assuming it's in the same plane (a likely situation).

BTW, using the 3 m/s accuracy of doppler measurements that had been state of the art recently, one could find close planets with masses even lower than this one. And since these observers have now demonstrated accuracies of 1 m/s, it should be possible to find close-in planets with masses less than 1 M_e.