* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Life on Other Planets
Astronomical unit wikipedia , lookup
History of Mars observation wikipedia , lookup
Aquarius (constellation) wikipedia , lookup
Life on Mars wikipedia , lookup
Geocentric model wikipedia , lookup
Planets beyond Neptune wikipedia , lookup
History of Solar System formation and evolution hypotheses wikipedia , lookup
Formation and evolution of the Solar System wikipedia , lookup
Definition of planet wikipedia , lookup
IAU definition of planet wikipedia , lookup
Dialogue Concerning the Two Chief World Systems wikipedia , lookup
Exoplanetology wikipedia , lookup
Planets in astrology wikipedia , lookup
Interplanetary contamination wikipedia , lookup
Circumstellar habitable zone wikipedia , lookup
Late Heavy Bombardment wikipedia , lookup
Rare Earth hypothesis wikipedia , lookup
Extraterrestrial atmosphere wikipedia , lookup
Comparative planetary science wikipedia , lookup
Astrobiology wikipedia , lookup
Timeline of astronomy wikipedia , lookup
Searching for Signatures of Life in Other Planets Assigned Reading Units 83 and 84 Final Announcements Exam # 3: grades are posted in the OWL Gradebook; solutions will be posted either today or tomorrow on the course website. Final exam: Tuesday, Dec 13th, in Hasbrouck Lab 20, at 10:30 am. Duration: 2 hours. Bring student ID Bring pencil # 2 Open notes/open book (no devices with wired/wireless connections) What is life? Theory A Working Definition of Life • Something that is alive – has both the instructions and the machinery for selfreproduction (either alone or in small groups). – metabolizes fuel and produces waste. – undergoes evolution through natural selection. • Note that this theory is based on what we have observed. Like all scientific theories it is open to modification given conflicting evidence. • Like all classification schemes there are some grey areas. – humans, animals, plants, bacteria are alive – viruses border on fringes of life • require other life-forms to reproduce • Have no mechanism for metabolizing energy • So far, all known Life on Earth is based on amino-acid molecules (proteins and DNA) – Based on 6 fundamental elements: hydrogen, carbon, oxygen, nitrogen, sulfur, and phosphorus; • Considered irreplaceable until the recent experiment of replacing phosphorus with arsenic in bacteria dredged from the bottom of the salty, arsenic-rich Mono Lake • Could we have silicon-based life (instead of carbon-based)? So how did life originate on Earth? Possibility #1: Life spontaneously generated on its own – Building blocks of life: water, ammonia, and methane, can combine to form amino acids, all present in Earth s early atmosphere and near volcanic activity. Possibility #2: Earth could have been seeded by life from space. – Simple amino acids are routinely found in space – Earth was not the first planet to form that could support life … and significant mass exchange occurred between planets early on. – Evidence that simple life forms could survive long trip buried in meteors. Possibility #3: ? The Most Likely Place to Find Extraterrestrial Life? Definition: The Habitable Zone There is a region around each star where the average temperature of a planet falls between 0 ºC and 100 ºC. The planets with orbits contained in this region can support liquid water. Venus Earth Mars habitable zone Jupiter Solar System Planets Venus Climate History • Although Venus and Earth are believed to have started with the same amount of volatile gases, they followed very different evolutionary paths. • The early Venus may have been habitable with water oceans • However, the Sun s luminosity increased by 30% over the past 4 billion yrs. Venus water was most probably lost to space via a runaway greenhouse effect – Venus closer proximity to the Sun increased the amount of water vapor and CO2 in its atmosphere, which enhanced the greenhouse effect in a positive feedback loop – Over billions of years, Venus may have lost an ocean of water this way. Mars Climate History • Mars may have had a much warmer climate in its past – Geological evidence from erosion patterns suggest that liquid water was stable on the surface. • Warming was probably due to an enhanced greenhouse effect. – A CO2 atmosphere at 400 times present density would works for the present Sun • Volcanism may have been a source of CO2 – However, the faint young Sun would require that Mars had an extra means of warming the surface. • Methane [CH4] has been postulated as the missing greenhouse gas • Source of CH4 for early Mars? Other Possible Locations of Life in the Solar System • Mars is our best candidate for having life early on, just after its formation (Earth has fossil-evidence of life 3.8 billion years ago) • Europa (Jupiter moon): water under its surface! – Cf Lake Vostok in Antarctica • Titan (Saturn moon): thick atmosphere, nitrogen, possible oceans of methane, but no water and very cold! Origin of the Terrestrial Atmospheres • Terrestrial planets did not capture their own atmospheres – Too small and warm – Our atmospheres are considered secondary • Instead, terrestrials were enriched with impact delivered volatiles. – Water, methane, carbon dioxide and other gases were trapped in the Earth s interior rock • Venus and Earth, forming relatively close together in the solar nebula, probably started with a similar inventory of volatiles. What Kind of Life Could be Out There? How Many Planets out there? There are about 500-600 known planets circling around other stars (other than the Sun). Many are likely to be barren (too hot or too cold), but some may be `habitable . Habitable = a narrow region of orbits around a star where water can be in liquid form Future NASA (and other) missions may establish whether this is the case, but in order to do that, we need to understand how we recognize that a planet may host some life. What are the Biosignatures of Life? Different Forms of Life • Simple primitive life – single celled organisms (Prokaryotes) • Advanced multi-celled life – animals, plants, etc. (Eukaryotes) • • Intelligent Life – has ability to reason and create. Advanced Civilization – has ability to organize, create as a group. Other Planets OGLE-2005-BLG-390Lb A Earth-size planet rotating around a red dwarf star (low-temperature star), very cold (-364 F), with an orbital period of about 10 years. The planet-star system is located about 6100 lyrs from the Earth, towards the Galaxy s bulge. XO-1b Located 600 lyrs from the Earth, this planet is orbiting (in 4 days) a sun-like star, in the constellation Corona Borealis. What are we likely to `see • We will not be able to see the extrasolar planet • Everything we learn about the planet will have to come from `obvious characteristics • The signs of life must be a global phenomenon Detecting Distant Signs of Life Life can provide global-scale modification of (GAIA hypothesis): – A planet s atmosphere – A planet s surface – A planet s appearance over time Astronomical Biosignatures • Features in spectra indicative of life. • Must be global-scale, and they need to be easily separated from the central star. H 2O H 2O Planetary Environmental Characteristics • Is it a terrestrial planet? (Mass, brightness, color) • Is it in the Habitable Zone? (global energy balance?, type of star?) • Does it have an atmosphere? – clouds, possibly surface – Greenhouse gases: CO2,H2O vapor present? – UV shield (e.g. Ozone [O3])? • What are its surface properties? – Presence of liquid water on the surface – Land surface cover ? G. Chin GSFC The Planet We Know and Love Atmospheric Greenhouse Effects σTa4 σTs4 Fo (1-a) The atmosphere is sufficiently transparent at solar wavelengths to allow some sunlight to penetrate to the surface – Ozone and water vapor are primary absorbers σTa4 σTs4 - σTa4 The atmosphere is (partially) opaque at thermal wavelengths, reducing escape of heat to space – Water vapor, CO2 and Ozone are the primary absorbers Carbonate-Silicate Cycle • Planetary processes can regulate the atmospheric greenhouse gas concentrations – Atmospheric CO2 dissolves in the ocean – Rainfall erodes silicate rocks and carries it to the oceans – The silicate minerals react with the dissolved CO2 to form carbonate minerals which fall to the ocean floor – The sea floor carbonates are eventually subducted – The subducted rocks melt to form CO2 rich magma, which is released to the atmosphere in volcanic eruptions. CO2 The Photosynthetic Red Edge Life Changes a Planet s Surface Harry Lehto Harry Lehto The Effect of Surface Type in the Visible: Got Life? Crisp, Meadows In Summary • We need to understand the history of our own Solar System planets, to interpret data from exoplanets. • First and foremost, we need to understand how the Earth (the only planet we currently know to host life) `looks from the `outside . • There are many known exoplanets, although we don t know if any is hosting life (unlikely, as they orbit too close to their stars). • Future space missions may give us more planets, and the answer to `alien life.