Scientists are busy
looking for other planets like our planet. So far they have
discovered some 889 planets. In addition, there are some 2712
“candidate planets.” These are cases where we have some data
indicating that a planet probably exists at a particular place, but
the data is not quite strong enough for scientists to conclude that
the planet definitely exists.
Most of these planets have
been discovered by the Kepler Space Telescope, which unfortunately
has recently suffered a mechanical glitch which has put it out of
service for the time being. But scientists will be busy for years
analyzing the huge amount of data that Kepler has already collected.
Even if the Kepler Space Telescope takes no more observations, it
will be regarded as one of the greatest success stories in scientific
history.
The Kepler Space Telescope
mainly uses a technique called the transit technique. This technique
is so simple that you could illustrate it to someone by using a light
bulb and a rubber ball. Take the lampshade off a lamp, and tell
someone the light bulb represents a distant star. Then revolve the
rubber ball around the light bulb. Then ask the person, “How does
your observation of the light bulb change when the ball passes in
front of the light bulb?” The answer is that the observer sees less
light from the bulb when the ball passes in front of it. The same
thing happens (on a much different scale) to a telescope looking at a
distant star when a planet passes in front of the star – for a
short time a little less light is observed from the star. By taking
repeated observations of a distant star over several years, and
carefully analyzing dips in light from the star which occur at
periodic intervals, scientists can detect planets around other stars.
By exactly how much the light from the star dips, scientists can
estimate the mass of these extrasolar planets.
What astronomers are most
hoping to find are potentially habitable planets – planets that
could support the existence of intelligent life. To be potentially
habitable, a planet must not be many times smaller than our planet or
many times larger than our planet. If a planet is too small, it
won't have enough gravity to hold an atmosphere. If the planet is too
many times larger than Earth, it would presumably be a planet similar
to the gas giants in our solar system (Neptune, Uranus, Saturn and
Jupiter), which don't even have solid surfaces. To be potentially
habitable, a planet must also be in a zone that is neither too close
to the star which it revolves around, nor too far away from the star.
This zone where planets are not too hot and not too cold has been
called the Goldilocks Zone (after the famous story for children in
which a little girl rejects one bowl of porridge because it's too
hot, another because it's too cold, and finally picks a third bowl of
porridge which is just the right temperature).
The image below shows the
current state of the search for habitable planets. So far astronomers
have found 10 potentially habitable planets. Their relative sizes are
shown below. All of these planets are in the Goldilocks Zones of the
stars they resolve around.
The decimal number under
each planet is an estimate of how similar to Earth the planets are.
The closest matches (with a similarity index of .82) could well be
very similar to Earth. We will apparently have to
wait until 2017 for the next great breakthrough in finding
potentially habitable planets. In that year NASA will launch the
Transiting Exoplanet Survey Satellite (TESS). It
will have capabilities much greater than that of the Kepler Space
Telescope. Some predict that this satellite will be able to discover
between 1000 and 10000 planets.
No comments:
Post a Comment