Transcript Document

Advances in contemporary physics
and astronomy --- our current
understanding of the Universe
Lecture 8: Are we Alone?
May 28th, 2003
Extraterrestrial life at Earth?
•Found in December 1984 in
Antarctica by a U.S. meteorite-hunting
expedition.
•weighed about 4 and 3/4 pounds and
was shaped like a rounded brick or a
large potato, about 6 inches long by 4
inches by 3 inches.
Mars Rock ALH84001 which
contains rounded globules of
carbonate minerals. The
possible martian fossils are in
these carbonate globules,
leading to possible Evidence
for Ancient Life on Mars
• inner color of ALH 84001 is green.
• We know it (and about a dozen other
meteorites) comes from Mars because
it contains traces of gas that is just like
the martian atmosphere obtained from
Viking project.
Exploration to Mars
Viking project: First Search for
Life
• The Viking project consisted of launches
Orbiter and Lander
of two separate spacecraft to Mars, Viking
1 and Viking 2. Each spacecraft consisted
of an orbiter and a lander.
•Viking 1: launched on 08/20/1975,
arrived at Mars on 06/19/1976 and landed
on Mars on 07/20/1976.
•Viking 2, launched on 09/09/1975,
arrived at Mars on 08/07/1976 and landed
on Mars on 09/03/1976.
• Image of the entire surface of Mars at a
resolution of 150 to 300 meters, and
selected areas at 8 meters are obtained.
Viking’s scientific experiments
•Physical Properties
•Imaging
•Atmospheric Structure
•Seismology
•Biology
•Magnetic Properties
•Gas Chromatograph / Mass
Spectrometer
•Radio Science
•Meteorology
•Neutral Mass
Spectrometer (NMS)
•Retarding Potential Analyzer
(RPA)
•X-Ray Fluorescence
Spectrometer (XRFS)
Viking found no life in Mars and there was confusion
over early biological experiment results!
Other missions to Mars
Mars Pathfinder How do we scout Mars? Earth's
opposition to Mars in orbit occurs every 2 years.
Launching 2 small missions every opposition has
been our plan ever since the Viking spacecraft
observed it. Here is the schedule:
--1997 Mars Pathfinder, Mars Global Surveyor
(MGS)
-- 1999 Polar Lander, orbiter
-- 2001 Rover
--2003 Rover
-- 2005 Sample Return Mission
Round trip to Mars?
• Can we send men to Mars? The first step of space colony.
• Roundtrip possibilities? How to come back? No rockets.
• Expenses and Cost. NASA estimates ~ $100 billion.
• Fuel? Get fuel from Mars. 2H2+CO2 -> CH4 + O2
• Trip plans, Food, water, O2 , medicine, etc.
• Safety. How many crew members?
• First step on Mars probably after 2015.
Where are we in the Universe?
Origin of Life
•How does life form on Earth, or maybe it comes from space?
When the Earth was formed, there exist various primordial atoms.
Some of these atoms came to be arranged in the form of
molecules of DNA, which is the essential building block of life.
•Why the universe is such that life is possible?
The Anthropic Principle: If the conditions were not suitable
for life, we would not be asking why they are as they are. ----an idea originated P.A. M. Dirac
Definition of life
•What is(are) the essential character(s) of life?
•What differentiate us from say, robots?
The most important thing about DNA is
its ability to copy itself!
This makes reproduction possible.
Evolution and mutation are then natural
consequences of the copying process!
Being able to reproduce itself is the
most essential criterion for life!
The Intelligence
•Life has evolved in the
planet of Earth for the
past 4~5 billions of years.
• It took a rather long
period of time, two and a
half billion years, to go
from single cells to multicell beings, which are a
necessary precursor to
intelligence.
•The evolution speeded up
after intelligence appears.
Life beyond solar system
• Are there lives beyond solar system?
• If there are, are they DNA based?
• Do they have intelligence?
• If they are intelligent, can we make contacts with them?
• Have we been visited by some of them already?
• Maybe we are descents of them?
Drake’s equation
"What do we need to know about to discover life in space?"
N = R* • fp • ne • fl • fi • fc • L
N = The number of civilizations in The Milky Way Galaxy whose electromagnetic
emissions are detectable.
R* =The rate of formation of stars suitable for the development of intelligent life
( #/yr).
fp = The fraction of those stars with planetary systems.
ne = The number of planets, per solar system, with an environment suitable for
life.
fl = The fraction of suitable planets on which life actually appears.
fi = The fraction of life bearing planets on which intelligent life emerges.
fc = The fraction of civilizations that develop a technology that releases detectable
signs of their existence into space (for example, radio waves).
L = The length of time such civilizations release detectable signals into space.
Drake’s equation (2)
R is the average rate
of star formation in
the galaxy, equal to
about 20 stars per
year (i.e. recent HST
observations of M16
showing star
formation sites).
fp is the number of
suitable suns with
planetary systems,
now thought to be
around 1/2 (i.e. 51
Pegasus discovery), a
value that has made
scientists optimistic about the possibility
of intelligent life elsewhere in the galaxy.
fs is the fraction of
stars that are
suitable suns for
planetary systems,
approximately 0.1
(most stars belong
to spectral type M
and are probably too small, whereas a few,
such as O and B stars, are too short-lived).
The circumstellar disk around Beta Pictoris
ne is the mean
number of planets
that are located
within the
Continuously
Habitable Zone
(assuming liquid
water is necessary for
is evidence of planetary formation.
life)
Drake’s equation (3)
fl is the fraction of
such planets on
which life actually
originates (given
enough time
primative organic
substances will be
synthesized into
DNA and RNA,
recent detection of the amino acid Glycene
in the ISM by radio observations).
L is the mean
lifetime (in years)
of an advanced
civilization
(because it
depends on the
NATURE of the
race of intelligent beings it is the most
uncertain factor in Drake's Equation)
fi represents the fraction
of such planets on which,
after the origin of life,
some form of
intelligence arises
(evolution probably
occurs wherever life
arises, and intelligence
has survival value of 1.0.
fc is the fraction of
such intelligent
species that develop
the ability and desire
to communicate with
other civilizations
(they construct radio
telescopes or laser
systems)
Project Phoenix
•Search for radio signals from nearby stars.
• In Southern hemisphere, Phoenix began
observations in February, 1995 using the Parkes
210 foot radio telescope in New South Wales,
Australia.
• In Northern hemisphere, a 140 Foot Telescope
at the National Radio Astronomy Observatory in
Green Bank, West Virginia was online from
September 1996 through April 1998.
The 140 Foot Telescope at
the National Radio
Astronomy Observatory in
Green Bank, West Virginia
• Phoenix only scrutinizes the vicinities of
nearby, sun-like stars. About 1000 stars have
been targeted. All within 200 light years (well
within our own galaxy).
Project Phoenix(2)
•In mid 1998, the
Phoenix project
moved to the world's
largest antenna, the
1,000 foot diameter
Arecibo Radio
Telescope in Puerto
Rico.
•Radio frequency
range: 1,000MHz to
3,000 MHz.
courtesy of the NAIC - Arecibo
Observatory, a facility of the NSF
•two three-week
sessions each year.
Allen Telescope Array
Problem: No funding and lack
of observation time.
Solution: Build dedicated
telescope and ask Microsoft for
money! (Paul Allen, and Nathan
Myhrvold are former co-founder
and CTO of Microsoft.
Because of its ability to study many areas on the sky at once,
with more channels and for 24 hours a day, the Allen Telescope
Array will permit an expansion from Project Phoenix's stellar
reconnaissance of 1,000 stars to 100 thousand or even 1 million
nearby stars.
The “WOW” event
•The Wow! radio emission
event entered the receiver of the
Big Ear radio telescope at about
11:16 p.m, Aug. 15, 1977.
• Location: right ascension was:
19h17m24s, declination was: 27 degrees and 3 minutes of arc
(- 27d03m): in the direction of
the constellation Sagittarius.
Unfortunately, no signals resembling the Ohio
State Wow were ever detected again.
Message from Earth
•
What are these Earthlings trying to tell us? The above message was broadcast from
Earth towards ther star cluster M13 in 1974. During the dedication of the Arecibo
Observatory - still the largest radio telescope in the world - a string of 1's and 0's
representing the above diagram was sent. This attempt at extraterrestrial
communication was mostly ceremonial - humanity regularly broadcasts radio and
television signals out into space accidentally. Even were this message received, M13 is
so far away we would have to wait almost 50,000 years to hear an answer. The above
message gives a few simple facts about humanity and its knowledge: from left to right
are numbers from one to ten, atoms including hydrogen and arbon, some interesting
molecules, DNA, a human with description, basics of our Solar System, and basics of
the sending telescope. Severalsearches for extraterrestrial intelligence are currently
underway, including Project Phoenix under the direction of Dr. Jill Tarter.
(http://antwrp.gsfc.nasa.gov/apod/ap970717.html)
Records on voyager
• Voyager 1 and 2 are launched on
August 20 and September 5, 1977.
Gold-plated phonograph records
contained in aluminum cases were on
board.
•The Voyager Record contains images,
sounds, and music of our planet
selected by a committee headed by Carl
Sagan.
The Voyager records were attached to
the outside of the Voyager 1 and 2
spacecraft. Contained in aluminum
covers, the records are expected to
survive in interstellar space for more
than 1 billion years.
Not the end
Are we alone?
•If there is no other life, then it sure is a great
waste of space(from the movie “contact”).
Future of Human kind: dreams are maps --Exploration of space and meaning of lives.
References
1. http://www.seds.org/~rme/drakeeqn.htm
2. http://www.seti-inst.edu/seti/seti_science/Welcome.html
3. Viking project:
http://nssdc.gsfc.nasa.gov/planetary/viking.html
4. Scientific results from Viking Project: Journal of
Geophysical Research, "Scientific Results of the Viking
Project", vol. 82, no. 28
5. About Martian meteorite ALH 84001
http://www.lpi.usra.edu/lpi/meteorites/The_Meteorite.html
6. Steven Hawking’s public lectures:
http://www.hawking.org.uk/lectures/lindex.html
References (2)
• Life in the universe: (a site of links)
http://www.phys.ufl.edu/~avery/html/seti.html
• On the “WOW” signal,
http://www.setileague.org/articles/calibwow.htm
• A site about Carl Sagan,
http://www.planetary.org/html/news/subjectarchive/Saganidx.html