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."

So...we found...?

Trio of Super-Earths Discovered

So we found more oil?

Re:So...we found...?

first we have to make sure that oil-producing GE microbes exist there

Really short periods

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

A short orbital period and a higher mass mean a greater possibility we can see the star shifting back and forth as the planet revolves around it. As our instrumentation and measurements get more accurate and precise we should be able to reliably infer the presence of smaller planets with longer orbital periods.

With how many large planets we're finding, it's pretty likely there are plenty of smaller earth like planets to be found when we gain the ability to do so.

Re:Really short periods

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.

So, time for a REALLY long-baseline telescope?

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?

Two problems with your suggestion. 1) Baseline is not the limit of any planet searches. 2) Planet searches are done with optical frequencies.
You could put a radio telescope on the moon and do VLBI - but not an optical telescope.
The most difficult part right now of detecting planets using Doppler shift is a fixed frequency standard to compare the stars spectrum against - they are measuring centimeter/second movements of the star. Baseline has nothing to do with the current limits. AFAIK, the only optical interferometer of any note is at Keck - and I don't even know if it has been used yet. See this article: http://optics.org/cws/article/research/33693 [optics.org]

Re:Really short periods

Because our primary method of detecting a planet right now involves looking at its gravitational effect on the star, and planets that have a lot of mass, are near to their star, and go quickly cause the greatest fluctuation in gravitational force.

Re:Really short periods

One of the ways we detect planets (not sure about the HARPS) is the measurement of the wiggle the parent star makes. The more massive the planet and/or the faster it orbits, the easier it is to detect the wiggle. Basically, the star will move either side to side or back forth from our vantage point (depending on the orientation of the orbit compared to our position), and this slight movement is used to calculate the mass, speed, etc of the orbiting planets. If the planet is orbiting side to side from our veiw point, we measure the speed the star moves side to side. For back and forth, we measure the slight doppler shift in light as it moves towards and away from us. Since closer planets tend to orbit faster, most of the planets we've discovered so far are large, close, fast-moving ones.

Again, this is only one way this is done, and I'm not sure about this particular planet. I can't make heads or tails of the HARPS link in any case.

Re:Really short periods

Whatever you do, don't try to answer this question by typing "really short periods" into Google. Trust me.

Re:Really short periods

As others have mentioned it is a selection bias. Part of this has to do with the detection method. What they do is look at spectral lines from the star to determine how fast it is moving as it 'orbits 'around the center of mass of the star-planet system (this is very close to the center of the star since the star is so massive, so it is more of a wobble than a straight orbit). The closer the planet is to the star, the larger the gravitational force, so the larger the velocity/ doppler shift. So it is easier to find planets with shorter periods. But even if we developed a new technique today that didn't depend on doppler shifts, we would still only find short period planets for the first few years. Why? Because you need to take measurements for at least a full period before you can determine with any accuracy that you're seeing a planet. So planets with 5yr or 10yr periods will not be confirmed right using any new technique, anyways.

And to add to another point made below, it is possible to have a planet with an orbital period measured in days which we could comfortably live on. A white dwarf star would be cold enough to allow for normal temperatures, even at distances closer than Mercury.

Such a downer...

Every time there's news of earth or super-earth sized planets, we always find that they're orbital period is like 5 days, which would mean the planet is completely scorched and incapable of supporting life or bearing liquid water. Such a downer....it doesn't matter what sized planet you have if its orbit places it so close to the star. Is this because the whole eclipse-detection method requires the planet to be close to its star so we can't actually detect planets further out from the star? I'm actually kind of tired hearing about "exciting" new of another planet being discover 5-30 million km from its star...that is not even close to being in the habitable zone people.

So...

What exactly makes these Earth-like? From the data it appears that their masses are several times greater than Earth and their orbital periods are much much shorter than Earth. Is it because the star they orbit is similar to Sol? Is there any indication of water or an atmosphere on any of them? Not that this isn't a cool find, but it seems that the use of the word "Earth" is just sensationalism. I would've been just as happy if they had simply said "three planets."

Re:So...

Does it help to think of it as a project fork?

Re:So...

The planets found are "earth-like" because they are believed to be rocky, terrestrial planets. Right now, we can only detect such small, lightweight planets when they are very, very close to their star.

The fact that we see so many of them gives some hope to the idea that there are many terrestrial planets out there and that some of them would be in the habitable zone. We can't yet see planets that might support life so right now we look for planets that share some characteristics with Earth, in this case size.

DNA proven right once again!

> ... and is located 42 light-years away ...

So that was why the answer to the ultimate question was 42 - and the ultimate question itself must be something like "Are we alone in the universe, and if not, how many light-years away is the nearest other life?"

That close to a sun-like star...

---they can't be very Earth-like. "Super-Mercury" would be more like it.

42 light-years away?

Space race just found a new meaning for its life, its universe, and everything.

Nothing Earthlike about these 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.

Anything orbiting a star in 4.3 DAYS is extremely close to the star, and could not possibly anything more than a cinder, probably at near rock melting temperatures.

Mercury has an orbital period of 88 days for comparison.

Re:So what exactly is

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

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...

Re:So what exactly is

> 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)

With orbital periods of less than three weeks around a sun-like star they are going to be hotter than Mercury: far too hot for life.

Re:So what exactly is

It's a planet devoted to fighting crime, and supporting truth, justice, and the American way.

Re:Not good for much

I think it's the "42 light-years away" that makes them less than useful.

Re:Please tell us more oh wise one

Interesting science they are doing over there. So lacking any evidence that planets are ubiquitous, and even worse that true Earth-like planets exist in the first place even though they can't yet detect them, they are ready to say that they must exist because they have now found some "smaller" hunks of mass orbiting a star?

This is sheer idiocy. Astronomers are finding planets all over our immediate vicinity in space - how more ubiquitious can you get than the current rate of discovery? It seems any star with metallicity has a planet or planet system around it. As for the second part - the only limitation in finding Earth sized worlds is detector sensitivity. Seeing how they can find individual objects larger than Earth, and comet sized and smaller debris (in bulk), it seems pretty obvious they will find planets with masses the size of Earth, or smaller, as soon as we can get the sensitivity down to that point.