Last time, we looked at the main asteroid belt, a feature of the solar system that makes the place we live so special. How special? Well, to answer that, I thought this time round, we’d dip our toes into the world of “recent discovery”. Doing so will emphasize just how much – and how little – is out there.
What do I mean? Let me explain using exoplanets.
What is an exoplanet?
An exoplanet – or extrasolar planet – is a world that orbits a star other than the Sun. Eg, one that lives outside of our own Solar System.
How many neighboring worlds are there?
The truthful answer? Since 1988, we’ve discovered more than 2000 of them.
More than 2000! Is that an accurate figure?
Oh yes. We can say this because astronomers are rather picky. Here’s what I mean: The Kepler space telescope has detected the majority of those candidate planets. Various factors go into determining if we’ve spotted a new planet or not, and as such, scientists realize about 11% of the results may be false positives.
So, what statistics are we actually looking at then?
Here’s the amazing thing. From the candidates selected, there is at least one planet on average per star. (Yes – I said 1 planet on average per selected star). About 1 in 5 Sun-like stars have an “Earth-sized” planet in the habitable – Goldilocks – zone, with the nearest residing only 12 light-years from Earth. So, we estimate there are about 200 billion stars in the Milky Way. That would give rise to 11 billion potentially habitable Earth-sized planets in our own galaxy alone, rising to 40 billion if planets orbiting the numerous red dwarfs are included. Do you see why this is so amazing?
Now, I know some might think, “Hang on, we messed up the figures.” And things like that do happen. So, here’s the way I stay positive. Just imagine the skeptics are right and we got the math all wrong. 90% wrong. Even so, there’d still be millions of potential homes out there. Awesome!
Yeah, but how many are home to actual solar systems?
You’ll love this…Since 1988, we’ve discovered more than 2085 planets in 1331 different solar systems. As of February this year, 509 of them are known to be multiple planetary systems. ☺ If that’s not deserving a “WOW!” I don’t know what is.
Are any of them like Earth?
To be fair, we shouldn’t expect that all the time. I’m a great fan of Star Trek, and although our fictional space explorers do tend to meet a lot of humanoid life forms, there have been instances where they’ve bumped into things so exotic, it stretches the imagination. In a way, I think that’s good. Life is life. It doesn’t have to be humanoid. And the statistics tend to show that. For example:
The least massive planet discovered so far is PSR B1257+12 A, (I know, dead sexy eh?) which is about twice the mass of the Moon. The most massive planet listed on the NASA Exoplanet Archive is DENIS-P J082303.1-491201 b. Denis is huge and possesses about 29 times the mass of Jupiter – although according to most definitions of a planet, that’s too massive to be a planet – and may be a brown dwarf instead. There are planets that are so near to their star that they take only a few hours to orbit and there are others so far away that they take thousands of years to orbit. In fact, some are so far out that it is difficult to tell whether they are gravitationally bound to the star in the first place…(Something we can attest to within our own solar system with one of our more recent discoveries, Sedna and 2012 VP113).
Have we ever spotted anything beyond our galaxy?
Well, here’s the thing. While 99.9% of the planets detected so far are within the Milky Way, there have been a few possible detections of extragalactic planets. I’m sure many of you will have noted with interest recent news items regarding astronomers’ assertions of the receipt of radio signals from beyond the galactic rim? Phew. Did ET try to phone home and miss?
If life is out there, what common denominator should we look for?
That’s easy. Water. The discovery of exoplanets has obviously intensified interest in the search for extraterrestrial life. What that life might resemble, is another matter. However, one thing most scientists – and common sense – agree on, is that we should show a special interest in those planets that orbit within in a star’s habitable zone, where it is possible for liquid water (and therefore life as we know it) to exist on the surface. The study of planetary habitability also considers a wide range of other factors in determining the suitability of a planet for hosting life, but accessible water is by far the overriding factor.
How come we’ve suddenly started to find so many planets? Is it easy?
No it’s not easy. But the equipment we use is becoming far more sophisticated with each passing year. Remember one of the examples I mentioned above, the one revealing the discovery of worlds that orbit their suns in a matter of hours? Those are incredibly hard to spot for all sorts of reasons, especially if you use visible light telescopes. Think about it, Planets only shine because of the light they reflect from the star they orbit. If a planet is too close – or the composition of its atmosphere too dull – it would be like trying to pinpoint a gnat flying next to a brilliant searchlight from miles away.
So, to overcome the glare given off by stars, astronomers use things like infrared space telescopes, or, they search for the effect exercised by a planet on its parent. Don’t forget, although the star holds a plant tightly in its gravitational grip, the planet also exerts an influence on the sun it orbits. (As well as causing a slight dip in its luminosity). Think of it as a gravitational dance. If you learn the steps, you know what to look for.
So, what does the future hold? Exciting times, that’s for sure. As some of you will no doubt know, NASA is working on more space missions that will allow scientists not only to find other solar systems but also to study the planets there in greater detail. Some of the intriguing questions these missions might help answer are how common the other solar systems are. I’m especially interested to learn how typical our own Solar System is. Remember, we have a layered defense structure to protect life: Our position within the Milky Way itself; giant outer planets like Jupiter; asteroid fields; rocky inner planets. Has any other world developed with such an impressive array of factors, and if so, are they like Earth; how do such “special” solar systems form and evolve; are there other planets out there capable of supporting life like ours?
Whatever the answers to such questions, we have an interesting few decades ahead of us. I don’t think it’ll be too long before bloggers will be posting the discovery of a truly Earthlike planet, and all the implications that will have. And if those radio signals I mentioned are anything to go on, who knows what else might be waiting?
Next time, we’ll concentrate on one of these latest developments, and emphasize why astronomy will be one of the ‘blue chip’ occupations of the future.
Keep looking up ☺