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

[EnOne]

The wobble allows us to find a star with planets to start with. In order to get detailed information about the planets composition it needs to pass between it's parent star and the earth. That way scientists can tell the difference between a rocky type planet 'super-earth' or a gas giant 'hot-Jupiter'. For example some one looking from outside our galaxy looking in would only see earth appear along a fairly narrow axis once every 365.25 days. The closer we would be to the sun the both the wider the viewable area of the earth passing between the sun and the observer, and the more often it would happen.

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?

[endstar]

This is the idea behind the "Space Interferometry Mission, PlanetQuest". You don't even need a very long baseline to make significant progress. If it goes forward (it has a troubled political history with NASA), it would be placed in an orbit around the Sun, trailing the Earth.

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

[naoursla]

There has been plans of creating interferometry telescopes that consist of multiple space craft separated by miles that use magnetic fields to adjust the disance between the spacecraft to focus the telescope.

http://en.wikipedia.org/wiki/Space_Interferometry_Mission

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

[Aaron Denney]

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

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

[drerwk]

When the GP talks about a long baseline, it is in reference to Very Long Baseline Interferometry. http://en.wikipedia.org/wiki/VLBI And the advantage is very high angular resolution. But to use VLBI you need to keep your (minimum three) telescopes phase locked. At radio wavelengths of a few cm and longer this is pretty easy to do. The signal can be recorded in a phase accurate manner. At optical wavelengths of a micron or smaller this is very hard to do. I know of no way at present to record optical signals in a phase accurate manner suitable to this application. For optical interferometry http://en.wikipedia.org/wiki/Astronomical_interferometer the instruments have to be close enough to pipe the light into a common observation location. This will not happen from the moon to earth.

Re:Nothing Earthlike about these planets

[Anonymous Coward]

I had a thought about this. What if the star is some very small dwarf? What would be the habitable zone for life in that case? Anyone know? Somebody with a basic knowledge of astrophysics can probably do a quick calculation to estimate the surface temperature of a rocky planet given a red dwarf's size and temperature.

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...

Why are we surprised??

[ndoggac]

Why are scientists/people surprised when they find new exo-planets? Let's see, there are at least 200 billion stars in our own galaxy (possibly up to 400 billion), and it is 100,000 light years in diameter. The Milky Way has 5 spiral arms, our solar system is located in the shortest arm, and our capability to locate exo-planets barely extends outside our own spiral arm. The record find right now is 17,000 light years away. So we can only see planets in a very small percentage of our own galaxy, let alone the estimated "hundreds of billions" of other galaxies! The one star we know the best (our sun) has 8-9 planets circling it. I'd be more surprised if they didn't find planets around almost every star they look at! There are more stars in the universe than there are grains of sand on the entire earth...

Sorry for not being funny, but

[drwho]

Sorry for not being funny, but I couldn't find an intelligent comment to attach this to, so it goes at at top level.

basically, my opinion is that it is within our reach to create a number of large telescopes that will exist roughly within the solar system, though possibly above and below the solar plane. These telescopes will be primarily automated, though a human team may need to be maintained ex-earth to do repairs and upgrades. All of these telescopes will be controlled by, and report to, all of the next generation super computers this race seems to be so good at creating (as opposed to high speed transportation systems). the ultimate goal is to be able to see the planets directly, and to observe and estimate the possibility for life as we know it (roughly). Where life does not exist, we seed it, though it may take generations to arrive, and thrive. This is our goal as a race, is to spread terran life as far as it can be spread. this is why the plants put up with us. It is our manifest destiny.