By Andy Lloyd ©
Astronomers are being kept very busy these days now that technology has allowed us to spot planets orbiting other stars. This technology is rapidly improving, with the prospect of the Keck interferometer searching out Earth-sized planets in the not too distant future. Right now, the game involves watching the minute wobbles of nearby stars and analysing them to ascertain the properties of the planets involved. Merely having discovering the existence of planets has re-ignited the debate about life in other star systems. Certainly, those who thought that planetary formation was a relatively rare event have been proven spectacularly wrong.
Astronomers are struggling to match currently accepted theories of planetary formation to the observations thus far. It has been a shaky time for this branch of astrophysics, as well as an exciting one. Science evolves through the emergence of new, challenging data, and no one predicted the information now under scrutiny. Part of the problem was that the current theories were based on a small data-base; our own solar system. Just as the data-base of life is currently limited to our planet. All that is about to change. The discovery of the first multiple planet system, Upsilon Andromeda, has brought forth verified data that implies that planetary formation is commonplace, with plenty of surprises.
This system holds 3 giant planets. The first is three-quarters of the mass of Jupiter and orbits only 0.06 AU from the star ( one AU is an Astronomical Unit, or the distance from the Sun to Earth). It traverses its circular orbit every 4.6 days! This verifies previous findings where giant planets were found to reside remarkably close to the parent star. We have always assumed that gas giants would have to form 4 AU or further from a star, to avoid the star’s “wind” literally blowing away the accreting volatile gases. Those planets within this limit are left with small atmospheres around rocky planetary cores, like the Earth. This latest finding, on top of the other extra-solar planets found residing in close proximity to their stars, bring this basic assumption into question.
The second planet around Upsilon Andromeda can be found about 0.83Au from the star (with a mass twice Jupiter’s), and the third resides 2.5AU from the star ( with a mass four times that of Jupiter). They both have elliptical orbits, another anomalous finding. It is now thought that most of the extra-solar planets have elliptical orbits, making our Solar system an exception rather than the rule. Those people advocating that our world is a special case in the galaxy could take some solace from this. After all, an elliptical orbit will create a planetary environment that is more extreme in conditions than ours. It will be interesting to see what the orbits of the Earth-like planets come out like when they are discovered.
But those doubting that the “12th planet” theory is impossible on the grounds that an extreme ellipse is too unstable an orbit for a planet should think again. Extra-solar planets are teaching us that to simply extrapolate theories, from our own Solar System as a data-base, is tenuous at best. Variety appears to be the spice of life out there in the cosmos.