Transcript Extra-Solar Planets continued

Announcements
• Observing on the roof of Van Allen Hall,
“clear sky patrol”, will begin on Tuesday,
September 7th. For that week, it will run
from Tuesday to Thursday from 9 pm to 11
pm on clear nights.
Planets beyond the solar system
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Yesterday’s news
Life
The habitable zone
Evolution of life on Earth
Communicating with intelligent life
Reading: all of chapter 27
Astronomers Spot Smallest Planets Yet
U.S. Astronomers Spot Smallest Planets Yet Orbiting
Nearby Stars, Trumping Europeans
The Associated Press
Aug. 31, 2004 — American astronomers say they have
discovered the two smallest planets yet orbiting nearby stars,
trumping a small planet discovery by European scientists five
days ago and capping the latest round in a frenzied hunt for other
worlds like Earth.
All three of these smaller planets belong to a new class of
"exoplanets" those that orbit stars other than our sun, the
scientists said in a briefing Tuesday. They define this new class by
the planets' smaller mass roughly 14 to 18 times the size of Earth
and equivalent to Neptune in our solar system.
Researchers don't know the composition of these new, smaller
planets or what they actually look like.
In our solar system, Neptune and Uranus are of similar size and
they are composed of an icy, rocky core enveloped in a thick
atmosphere of hydrogen and helium. But they sit in the farthest
coldest reaches of our solar system.
By contrast, both of the new planets are very close to their stars,
making them difficult to spot.
One of them orbits very close to the star named 55 Cancri, which
is about the same size as our sun and located 41 light-years away
in the constellation Cancer. The new planet was located by
University of Texas-Austin astronomers using the Hobby-Eberly
telescope in the Davis Mountains southeast of El Paso.
The star already had three known gas giant planets looping it in
orbits that take anywhere from 14 to 4,520 days. The new planet
is the innermost of the quartet, zooming around the star in 2.8
days from a distance of about 3 million miles.
Researchers acknowledged there probably are several different
types of solar systems orbiting distant stars. But for now, the 55
Cancri system bears the closest resemblance to ours.
55 Cancri
• Star 60% as bright as the Sun and only 5%
less massive than the Sun.
• Outermost known planet has an orbit similar
to that of Jupiter, but is 4 times the mass of
Jupiter.
• Inner 3 planets all lie within the orbit of
Mercury – one is about the mass of Jupiter.
The other new planet discovered by American scientists orbits a
star called Gliese 436, that lies about 33 light-years from Earth in
the direction of the constellation of Leo. This Neptune-sized
planet also sits 3 million miles from its star and whips around in a
tight circular orbit once every 2.64 days.
Besides the exoplanet's size, what makes the discovery
remarkable is that Gliese 436 is a red dwarf star that produces
only 2 or 3 percent as much light as the Sun. Stars in this
category account for 70 percent of the stars in the Milky Way
galaxy, but until now, astronomers had not believed that such faint
stars would yield new planets.
"We estimate there is something like 20 billion planetary
systems existing in our Milky Way galaxy alone," Butler said.
Two more exoplanets both gas giants also were spotted in the
past week. One was by the same European team using a
telescope in Chile.
The other was discovered by a U.S.-based team using a network
of small telescopes on California, Texas and the Canary Islands.
Instead of measuring star wobbles, they measured the tiny
amount that a star dims when a planet passes by in its orbit.
So, a total of 4 new planets were discovered (really
announced) last week.
What is Life?
• What are the essential characteristics of
life?
What is Life?
Essential elements are:
• Life reproduces itself
• Life is able to adapt and pass changes to
new generations
This seems to require a genetic code which
can stores information about how to grow
new organism and is passed from
generation to generation
Life on Earth
• Is based on `organic’ molecules – those
containing carbon atoms
• Carbon can combine with hydrogen and
other atoms to form complex molecules
• Complex molecules appear necessary to
store the information needed for a genetic
code
• Life on Earth uses DNA, a carbon-based
molecule, to store the genetic code
Life on Earth
• Life on Earth appears to require water
• No life is know to exist in the complete
absence of water
• Water allows other molecules to dissolve,
move around, and interact with each other
Habitable zone
• The requirement for water suggests those
planets which have liquid water may be
the most promising havens for life.
• In order to have liquid water, a planet must
be “not too cold and not too hot”, i.e. at a
temperature between freezing and boiling.
• How warm a planet is depends on its
distance from the sun.
Are there any exceptions to the
habitable zone?
• Yes, if there are sources of energy other
than the sun to keep a planet (or moon)
warm.
• Possible energy sources
– Radioactivity
– Tides
• Liquid water oceans are though to exist on
Jupiter’s moon Europa
Are 55 Cancri’s planets in the
habitable zone?
Evolution of Life on Earth
• Even if we find life on another planet, is it
likely to be a higher form of life such as
mammals or something simpler?
• What form of life occupied the Earth for
most of its history?
Evolution of Life on Earth
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4.6 billion years ago – Earth formed
3.96 “ “ “ – oldest rocks
3.5 “ “ “ – oldest fossils – single celled life
0.7 “ “ “ – multicellular life
0.0001 “ “ “ – humans (homo sapiens)
History of life on Earth in 12 hours
Carl Sagan’s “Cosmic Calendar”
The history of the Universe in one year
Big bang
Milky
Way
forms
Sun and Oldest
planets known
form
life single
cell
First
multicellular
life
Search for Extraterrestrial
Intelligence (SETI)
• We could avoid this whole business of searching
for planets and primitive forms of life, if
extraterrestrials would just send us a message.
• There are active searches for such signals, mainly
in the radio, some using visible light.
• One thing that is needed is more computing power.
You can volunteer your computer to process SETI
signals while the screen saver is on at the web site
http://setiathome.ssl.berkeley.edu/