Earth to...Earth? Are you there?

jasamaman writes "So far all the planets found outside our solar system have been gas giants. So they are not habitable, and couldn't really hold life as we know it. But "planet hunter" David Charbonneau is looking for another planet just like Earth, and claims that astronomers are "very close"."

Comments

Microlensing transit events

[Cally]

People have been looking for microlensing events caused by IIRC the transit that yielded the first atmosheric compostition numbers, last year, had already been found by the parallax ("wobbly star") method used to find 99% of other known extra-solar planets. The orbital plane was already known to be in line with us, and indeed the event's timing was predicted using the wobbling parent star. The point is that this technique (which is really a hack in the original sense) is only any use in those rare cases where the orbital plane intersects line of sight from the parent star to earth. Calculation of the percentage of orbits for which this is true is left as an exercise for the reader (cos I haven't the maths ;) [Source: Astronomy magazine.)

Why we haven't found them yet

[Anonymous Coward]

The sun of our solar system contains more than 99,9% of its mass. Of the remaining 0,1%, most is of the megaplanets like Jupiter and Saturn. Jupiter alone has around 500 times the mass of Earth. Habitable plants are thus incredibly, incredibly small compared to their suns or compared to gas giants. Given the limited funding (forget space, we need missile defense!) we can be happy that we can detect gas giants.

Close, but not that close

[Pedrito]

There are a number of ways Earth-sized planets could be discovered fairly soon (within the next 5-10 years). There are several planet-finding satellites to be launched. The Hubble would also be capable of detecting an Earth-sized planet passing in front of a star.

The real trick is finding the proper conditions. First, we need to find an extra-solar system in which Earth-sized planets exist. It's now believed that these are fairly few and far between. The reason is that a vast majority of the gas giant systems we've discovered so far have their gas giants in either really close orbits to their stars, or are highly eliptical with passes close to their stars. In these situations, Earth-like planets would likely be tossed into their stars, or more likely, tossed into open space, by the gravitational effect of the giants.

So, what you need is giants that live fairly far out (like Jupiter and Saturn). These appear to be about 1 out of 50+ systems. So, out of this 1-2% of systems, we then need to find ones with orbital planes that are parallel to our angle of view of those systems, and catch the Earth-sized planets passing in front of their stars.

Asking for all those conditions to line up is a pretty tall order, so it's unlikely we'll catch such an event in the next 5 years. My personal opinion. A large breakthrough may change that, and that's possible as well. After all, look at the discovery of extra-solar planets. It was a breakthrough idea that led to a sudden discovery of many of these systems, without a real technilogical breakthrough.

current methods dont see earth-size

[peter303]

Power-law distributions (more smaller stuff) suggest there should be lots of earth-size planets. However the current methods can only see fast-moving larger-than-Jupiter planets. The most popular method is measure faint doppler shifts over months to years. Terrestrial pectroscopic resolution limits this to about 10x Jupiters. Space-based methods may be more sensitive.

Another method is to look for eclipses of planets across the stars. This presumes (a) you are seeing another solar system edge-on, (b) you are lucky to catch the .0001% of time the planet is eclipsing, and (c) you aren't seeing a variable star like Algol. The US will soon launch a special telescope called Kuiper to watch one splotch of sky for five years continuously to catch planetary eclipses. Kuiper is notable for its 350 megapixel camera.

A third method is infra-red, which can see earth-size in newly forming planetary system dust-clouds. These would be too young and unstable to have evolved intelligent life on their own, but could be colony sites.

Re:How does he know...and isn't it done already?

[CyberDruid]

The closest thing that has been discovered is the two gas giants around 47 Ursa Majoris. This is the planetary system that so far looks most like our own. The two giants have less extreme (more circular) orbits than most of the ca 70 planets found, which also contributes to make it look a lot like ours. Gas giants can be an important contributor for life to appear on a smaller planet, since they act like magnets for asteroids and other debris, sheltering the smaller planets and giving life a chance to evolve.

Older Article

[Valdrax]

Actually, he's referring to this older Slashdot article, which you must've not read.

Now whether this formed in a vacuum or not is a technicality. The scientists shone high level of UV light on a chunk of ice containing ammonia and methyl alchohol at a temperature of 4K and found traces of 3 amino acids had formed. The amino acids themselves formed from the surrounding ice slurry which was in a vacuum, ergo "amino acids are formed in a vacuum."

It is NOT by parallax!

[Doctor Fishboy]

A small correction - most of the planets have been found by Doppler reflex motion of the parent star, not by the star's parallax. They're two VERY different methods.

Parallax determines the presence of an undetectable massive companion by the sinusoidal proper motion of the star system over a course of a few years. On the ground, you can do this for only a dozen of the closest stars (10 parsecs) or so.

Doppler reflex motion detects the companion by the Doppler shift in spectral lines in the parent star's spectrum as the planet/star orbit about their mutual centre of gravity. You can do this out to 100 parsecs or so.

HD209458 was a candidate from the Butler and Marcy Doppler survey that had a high inclination (edge-on) orbit. Brown and Charbonneau then did photometry to get the transit of the planet across the star's disk. Parallax did not come into it.

Dr Fish