Trio of Super-Earths Discovered

FiReaNGeL writes "A group of astronomers have now discovered a system of three super-Earths around a rather normal star, which is slightly less massive than our Sun, and is located 42 light-years away towards the southern Doradus and Pictor constellations. 'We have made very precise measurements of the velocity of the star HD 40307 over the last five years, which clearly reveal the presence of three planets.' The planets, having 4.2, 6.7, and 9.4 times the mass of the Earth, orbit the star with periods of 4.3, 9.6, and 20.4 days, respectively. 'The perturbations induced by the planets are really tiny — the mass of the smallest planets is one hundred thousand times smaller than that of the star — and only the high sensitivity of HARPS made it possible to detect them' says co-author François Bouchy, from the Institut d'Astrophysique de Paris, France. Clearly these planets are only the tip of the iceberg."

Comments

Really short periods

[Some guy named Chris]

Why is it that most of the planets discovered have extremely short orbital periods compared to our own? Is it because those are the easiest types to detect, or is it because we are a cosmic oddity with our slow orbit around our star?

Also, I wonder if one were on one of these planetary speedsters, would you be able to tell you were whizzing around your star so fast.

Re:Really short periods

[Cinnamon Whirl]

From TFA: "This star also hosts a Jupiter-like planet with a period close to 3 years"

Not actually the same star as above, but it shows even longer orbital periods can be detected if the planet is large enough.

Re:Really short periods

[maynard]

Here is what JPL says of the about the techniques used to find planets:

http://origins.jpl.nasa.gov/library/exnps/ch04_1.html#4.4

Based upon this I will offer these answers to your questions, though with the caveat that I am not an astronomer.

Astronomers are looking for perturbations in a star's light output intensity or in its lateral movement relative to other known stars.

What does this mean?

If a planet crosses the boundary between the star and us it should dim the light output. If this happens repeatedly at predicted intervals, a planet has been discovered. Similarly, if the star "wobbles" in a predictable manner, the gravity of the planet can be said to be "tugging" at the star. In both cases, one can determine (with a large margin of error) the mass of the planet by noting either the drop in light intensity or by comparing the known mass of the star against it's relative gravitational shift (wobble).

So: your question is, why do the planets thus discovered have relatively short orbital periods? My speculation is that it's much easier to determine short periodicity than long periodicity, thus outer planets orbiting remote stars should take far longer to confirm due to the need for lots of redundant data collection to confirm a finding.

Re:So what exactly is

[wile_e_wonka]

From TFA:

"With the advent of much more precise instruments such as the HARPS spectrograph on ESO's 3.6-m telescope at La Silla, we can now discover smaller planets, with masses between 2 and 10 times the Earth's mass," says Stéphane Udry, one of Mayor's colleagues. Such planets are called super-Earths, as they are more massive than the Earth but less massive than Uranus and Neptune (about 15 Earth masses).

Re:So what exactly is

[Vectronic]

I think it just means its relatively solid, ie: non-gasious, plus they may deem it to be in the proper "zone" to become an earth-like planet (not too close, not too far)

Im not expert, but they (or at least one) may have an atmosphere of some sort, but I dont think anything that revolves around its sun that quickly, is likely to have "life", at least not intelligent life, they would have to be stupid yet productive, like insects...

So, time for a REALLY long-baseline telescope?

[OmniGeek]

Gee, if we had a telescope array with a baseline of, say, the radius of the Moon's orbit, then we could resolve some REALLY small orbital perturbations, vastly improving our ability to identify planetary systems.

It occurs to me that such a system wouldn't even need to be (continuously) staffed after installation, just the occasional maintenance call.

I think I see an opportunity for a Lunar observatory project...

Re:So, time for a REALLY long-baseline telescope?

[Aaron Denney]

Why can't we put an optical telescope on the moon?

Unusable as is...

[MiniMike]

but maybe when we get there we could turn them into 20.3 Earth-sized planets in a decent orbit. We could also take the extra 0.3 and make a moon for each planet, or maybe something fancy like a ring. Who knows, by the time we actually figure out how to get there, we might be able to do this too...