Monday, December 28, 2009

2010: Finding Earth-Like Planets

According to Alan Boyle, MSNBC, starting in January, scientists who have been studying the data collected by the Kepler Observatory will begin to report on what rumor suggests will be the first dozen of what will be potentially thousands of extrasolar planets revealed over the next three years.

Scientists are on their way to discovering thousands of new planets, potentially including hundreds of worlds the size of Earth, in Earth-like orbits around sunlike stars. They expect to achieve that goal within three years or so. But they'll start with the weirdest worlds.

(See: MSNBC: Looking for Alien Earths? Here They Come.)

So far, over 400 planets have been discovered orbiting other stars. However, our detection methods have favored larger planets and those that are closest to their parent stars. This means that we have mostly discovered 'hot Jupiters' - planets the size of Jupiter and larger - much larger - orbiting close in to the star.

The Kepler Observatory also favors finding planets close in to their parent star. However, it is capable of discovering planets the size of earth. So, this first batch of planets to be reported will likely include a number of hot Jupiters. However, it will also include some super-hot Venus-like planets.

They will still be too hot to expect to hold any life. However, those planets will come. Each time another set of data is downloaded from the Kepler Observatory, scientists have the opportunity to confirm planets that are further and further away from the parent star.

The Kepler Observatory finds a planet by measuring the change in brightness as the planet orbits the parent star. As the planet passes in front of the star, the star gets a little bit dimmer. Kepler records these dips in brightness. Three dips in brightness over a regular period tells scientists that the dips were caused by a planet that had passed on front of the star three times.

Scientists want to see the brightness dip three times before they will suggest that a planet is responsible. This means, with 45 days' worth of data, scientists can discover planets that orbit their parent star in 15 days or less (hot Jupiters and hot Venuses).

With 1100 days worth of data, scientists can discover planets that take a whole year to orbit their parent stars - planets very much like Earth.

However, we do need to add the fact that our sun is a particularly large star. The vast majority of stars are smaller and cooler. As such, any wet planets or wet moons orbiting those stars will have smaller, tighter orbits. The discovery of those planets will take less than three years.

One more interesting fact to consider. A planet has to be in an orbit that lines up with the Earth for Kepler Observatory to detect them. That will be rare. For every earth-like planet that Kepler can discover, there can be hundreds that do not line up correctly.

Not only is Kepler able to discover planets orbiting other stars, it can discover moons orbiting those planets, if the moons are large enough. It may well be that, where life is possible in another solar system, it will be on a large wet moon orbiting a Jupiter-like planet, rather than on a planet like Earth.

All of this holds out the hope that the year 2010 will see some very interesting discoveries - with the discoveries getting more and moe interesting every year thereafter - culminating in the potential discvery 3 to 5 years from now of an Earth-size planet (or a wet moon) orbiting a parent star at just the right distance for liquid water, potentially with signs that its atmosphere contains heavy concentrations of nitrogen and oxygen,

That will be a very interesting day indeed.


mikespeir said...

Our Sun is a particularly large star? Huh?

Alonzo Fyfe said...

The vast majority of stars are red dwarfs. In fact, the number of stars in the Milky Way is variously estimated at between 200 billion to 400 billion, depending on how many red dwarfs there are, which is substantially unknown.

The larger and brighter a star becomes, the less common they are.

Estimates are that 92% of all stars are smaller than the sun. (8% of all stars are as large or larger.)

Within 20 light years of earth, there are 3 stars larger than the sun, 6 at about the same size as the sun, and over 100 that are smaller than the sun.

However, larger stars are certainly brighter. So, compared the stars that illuminate the night sky - that we can see with the unaided eye our sun is relatively modest. However, the stars that we can see are the top few percent of all the stars that exist. The stars we can't see because they are too small and too dim are far more common.

Anonymous said...

The vast majority or stars are therefore red dwarfs. Planets in the goldilocks zone may well be gravitationally locked to the parent star with their years being tens of Earth days long. I suspect lifeforms on such planets may well turn out to be the most common form; very different from us. For instance, I suspect vegitation will have its chlorophyl colour probably peaking toward the red end of the spectrum; making its grasses perhaps appear orange or yellow rather than green?? These worls would be very colourful compared with Earth. Animal eyes would also have a spectral response moving toward the red end I suspect. Has anyone performed any research into this?