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Hello, my name is Connie Chan and my project is on Possible Planets Found Around Nearby
Sun-like Star. The possible planets are called exoplanets or extra solar planets, which means
planets outside of our solar system.
Most astronomers believe that every star has planets and they are constantly searching
for exoplanets. Recently astronomers discovered a planetary system orbiting a nearby star,
Tau Ceti, it is the closest single star that resembles our Sun. It has the same spectral
class as our Sun, and it is about 12 light years away. Astronomers recently discovered
five planets orbiting this star, and one is in its habitable zone. In the picture, the
top portion is our solar system and the bottom is the Tau Ceti System. The green area are
the habitable zones for the two systems. The habitable zone is also referred to as the
Goldilocks Zone, because that is the area where the temperatures are just right for
supporting liquid water. Although it looks as though exoplanets E and F are in the Goldilocks
zone, astronomers are saying that exoplanet E is more likely to be habitable than exoplanet
F because it is more Earth-like.
Current potential habitable exoplanets. Tau Ceti is not the first star astronomers have
found with a planetary system, it is just the closest. ESI is the Earth Similarity Index,
and as you can see, Earth is listed at 1, and Mars is at 0.66. If a planet is a 1 on
the ESI, that means that it is identical to Earth. Earth-like planets are planetary bodies
with a similar terrestrial composition and a temperate atmosphere. Planets with over
a 0.8 on the ESI is rocky in composition and its atmosphere is suitable for most terrestrial
vegetation including complex life. Planets with an ESI of 0.6 to 0.8, like Mars, could
be habitable, but only by simple extremophilic life because those planets are probably too
cold or too hot. An extremophile is an organism that thrives in physically or geochemically
extreme conditions that are detrimental to most life on Earth. Tau Ceti e is listed as
number 6 in the order of similarity to Earth. It is under 0.8, so it might not be habitable
for complex life, but it can be habitable for extremophile forms.
There are more than 6,000 observations of Tau Ceti, and 3 instruments used to observe
that star. One of the telescopes was HIRES on the Keck I telescope from the W.M. Keck
Observatory in Hawaii. HIRES, which stands for the High Resolution Echelle Spectrometer,
is the largest and most mechanically complex of the Keck's main instruments. It breaks
up incoming starlight into its component colors to measure the precise intensity of each of
thousands of color channels. The bottom left picture is the interior of the Keck I telescope.
Using HIRES, astronomers detected a distant galaxy powered by Primordial cosmic fuel,
here's a picture of it on the bottom right. It means that they detected cold streams of
primordial hydrogen, matter left over from the Big ***, fueling a distant star-forming
galaxy. This gas flow is believed to be crucial in explaining the early Universe, and gives
us more insight to how our galaxy was formed.
Another telescope that was used is UCLES, which stands for the University College London
Echelle Spectrograph. It is on the Anglo-Australian Telescope in Australia. UCLES is a cross-dispersed
Echelle spectrograph located at the coude focus, which offers high resolution combined
with good wavelength coverage. At the beginning of the year, CYCLOPS2, a Cassegrain fibre-feed
for the spectrograph was added to the UCLES spectrograph. This updated fibre-bundle improves
the spectral resolution of the spectrograph, and it replaces the coude focus. This spectrograph
is primarily used to discover extra solar planets.
The HARPS spectrograph from the European Southern Observatory, is located in Chile. HARPS stands
for High Accuracy Radial velocity Planet Searcher and is dedicated solely to the discovery of
extra solar planets. It is an echelle spectrograph and is fibre-fed by the Cassegrain focus of
the telescope in La Silla. It is contained in a vacuum vessel, pictured at the top left,
to avoid spectral drift due to temperature and air pressure variations. It has two fibre-feeds,
one which collects starlight while the other is used to simultaneously record a reference
spectrum or the background sky. In 2008, HARPS spectrograph discovered a family of three
planets orbiting a Sun-like star 42 light-years away, and is pictured on the top right, but
these three exoplanets are too close to the star to be habitable.
The discovery of the planetary system orbiting Tau Ceti is important because it reinforces
astronomers' belief that every star has planets. There have been more than 1000 exoplanets
discovered, and it is estimated that there are 17 billion Earth-like planets. If these
predictions are correct, then there are more planets in the universe than there are stars.
It is also important because of its similarities and stability. Because of the
similarities to the sun it is the targeted for the Search of Extra-Terrestial Intelligence. The discovery
of extra solar planets has intensified interest in the search for extraterrestrial life as
well as the search for habitable planets. This explains why there are so many telescopes
dedicated to finding extra solar planets. This is a picture of an artist's interpretation
of the Tau Ceti system.
Quiz
What makes a planet habitable and why are those planets important?
On the Earth Similarity Index, what is the range a planet must fall under to host extremophile
organisms? And why? What are Earth-like planets?