Looking for ExoplanetsVIII

SummaryAre We Alone?

Jim Rauf

1OLLI Fall 2021

Looking for Exoplanets

• Introduction• Definition• Some history• A few equations• Universe• Galaxy• Solar System

• History• Number of Exoplanets

• Why Look• Science/curiosity

• Finding Exoplanets• Problem-Distances• Physics• Determining distances

• Search Methods• Radial Velocity method• Transit method• Direct Imaging method• Gravitational Lensing method• Astrometry

• Instruments for Exoplanet searches• Land based telescopes• Space based telescopes• Planned space based telescope - JWST

• Exoplanets Found-to Date• Some details

• Are We alone?

2OLLI Fall 2021

Looking for Exoplanets –Some Physics

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emission lines

absorption lines

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Gravity-it’s not just a good idea--- it’s the Law

Looking for Exoplanets –Methods

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54

3,440 1896

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Looking for Exoplanets- Properties of Stars

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Looking for Exoplanets-Mass of Stars

• Once the distance of the nearby star is calculated, its mass can then be determined

• First, the apparent luminosity of the star, or how bright it is as seen from the Earth, is measured

• Since brightness, or luminosity, is directly related to mass for a given star type (Hertzsprung-Russel diagram), the calculated brightness can be used to determine its mass

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Looking for Exoplanets - Status

NASA data (11-9-21)

• 4,566 confirmed exoplanets • 7,913 candidate exoplanets• 3,385 planetary systems

Discovery Methods• Astrometry 1• Radial Velocity 896• Transit 3,440• Microlensing 118• Imaging 54

Planet Types

• Neptune-like (1,546)

• Gas Giant (1,445)

• Super Earth (1,402)

• Terrestrial (168)

• Unknown (5)

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Looking for Exoplanets – Are we Alone?

8OLLI Fall 2021

Looking for Exoplanets – Are We Alone? – Some Numbers and Facts

9OLLI Fall 2021

Looking for Exoplanets – Are We Alone? – Some Numbers and Facts

• The universe is REALLY BIG• About 46 billion light years radius

• Search for Exoplanets has been in a small part of the Milky Way Galaxy

• Andromeda Galaxy , comparable size to the Milky Way Galaxy a, is 2 million light years away

• Estimated number of stars in the Milky Way Galaxy is 100 to 400 billion

• Estimated the number of galaxies in the visible universe is 100 to 200 billion

• Based on the Exoplanet data the number of planets is around around 10^25 planets

• Estimated number of habitable planets• Around M dwarf stars 4 to 5 trillion• Around Sun like stars 0.2 to 0.3 trillion

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Milky Way Galaxy is about 100 thousand light years across

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• Formulated in large part by the U.S. astrophysicist Frank Drake, it was first discussed in 1961 at a conference on the “search for extraterrestrial intelligence” (SETI), held at the National Radio Astronomy Observatory in Green Bank, W.Va.

• The equation states

• The factor R* is the mean rate of star formation in the Galaxy• fp the fraction of stars with planetary systems• ne the number of planets in such systems that are ecologically suitable for the

origin of life• fl the fraction of such planets on which life in fact develops• fi the fraction of such planets on which life evolves to an intelligent form• fc the fraction of such worlds in which the intelligent life form invents high technology capable at least

of interstellar radio communication• L, the average lifetime of such advanced civilizations

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Looking for Exoplanets – Are We Alone? – Drake Equation

OLLI Fall 2021

Looking for Exoplanets – Are We Alone? – Drake Equation

• These numbers are poorly known, and the uncertainty increases progressively with each factor on the right-hand side of the equation

• Widely quoted but at best vaguely known values for these factors are: • R* = 10/yr• fp = 0.5• ne = 2• fl = 1• fi=0.01• fc = 0.01

• This yields N = L/10

• If civilizations destroy themselves within a decade of achieving radio astronomy, a marker of an advanced civilization, then N = l, and there are no other intelligent life forms in the Galaxy with whom terrestrial researchers can communicate

• If, on the other hand, it is assumed that one percent of the civilizations learn to live with the technology of mass destruction , then N = 1,000,000

12OLLI Fall 2021

Looking for Exoplanets – Are We Alone? –Fermi Paradox

• In 1950 Enrico Fermi and colleagues were discussing the existence of alien life

• Fermi asked : “Where is everybody?”

• If there were civilizations scattered across the stars by the billions, why haven’t we heard from them?

• The Milky Way is about 10 billion years old and 100,000 light-years across

• If aliens had spaceships that could travel at 1 percent of the speed of light (~67 million mph), the galaxy could have already been colonized 1,000 times

• The Milky Way Galaxy could be crossed in ~10 years

• Why haven’t we heard from any of them?

• After hearing Enrico Fermi utter his paradox at Los Alamos, the physicist Leo Szilard immediately answered, “they are among us and they call themselves Hungarians”

13OLLI Fall 2021

Looking for Exoplanets – Are We Alone? – SETI

• The Search for Extraterrestrial Intelligence (SETI) was launched in the 1960s

• NASA joined in SETI efforts at a low-level in the late 1960s and early 1970s

• On Columbus Day in 1992, NASA initiated a formal, more intensive, SETI program

• Less than a year later, however, Congress canceled the program

• SETI has not produced definitive results

• Radio signals from exoplanets:• Light from the Sun has an intensity of about 1378

watts/ square meter at Earth• Electromagnetic radiation, light, radio signals , etc

travel at the speed of light• 186,000 miles/second in space

• A radio signal of 1 million watts from an exoplanet 40 light years away would have a signal intensity at earth of about 6.98 E-30 watts/ square meter• Inverse square law applies

• The signal would take 40 years to reach earth• A response would take another 40 years• Signals from more distant planets would have even

lower signal intensity• To send high power radio signals long distances would

require large amounts of power (money)• What is the motivation for intelligent beings on

exoplanets ?

14OLLI Fall 2021

Looking for Exoplanets – Are We Alone? – Some Numbers and Facts

• The Solar system has one planet with intelligent life- Earth

• It has four Terrestrial (rocky) planets

• Three of the four are in/near the habitable zone

• One has a breathable atmosphere, liquid water on its surface, a magnetic field deflecting Solar particles and cosmic rays

• Its mass and gravity are sufficient to retain its atmosphere

• Its atmosphere is mostly nitrogen (78%) with oxygen (21%)

• Oxygen is replenished by land and marine plant life CO2 to O2

• Oxygen is a reactive element forming oxides

• Earth has a large moon that stabilizes its axis of rotation

• Earth and the Sun are about 4.5 million years old

• Earth’s period of high volcanic activity ended millions of years ago allowing development of a life supporting atmosphere

• Earth’s orbital position in the solar system and its greenhouse effect yield a temperature of about 60 F

• For Earth type life to exist on other planets most , if not all , of these conditions must exist

• Just having an exoplanet that is Earth like in its size, mass, location in a habitable zone is not enough to develop life let alone intelligent life

15OLLI Fall 2021

Looking for Exoplanets – Are We Alone? –Some Numbers and Facts

• Earth spins around its orbital axis, changing its angle toward the sun — its obliquity — by a little more than a degree over the course of thousands of years

• These small differences are significant enough to cause the ebb and flow of ice ages

• The moon has long been recognized as a significant stabilizer of Earth's axis

• Without it, astronomers have predicted that Earth's tilt could vary as much as 85 degrees

• In such a scenario, the Sun would swing from being directly over the equator to directly over the poles over the course of a few million years, a change which could result in dramatic climatic shifts

• Such shifts have the potential to affect the development of life

• There is evidence that the axis of Mars , which has no large moon , has had its axis swing from about 25 degrees to about a 60 degree tilt in the past

16OLLI Fall 2021

Looking for Exoplanets – Are We Alone? CETI in the Milky Way

• A perspective on the likely number of Communicating Extra-Terrestrial Intelligent (CETI)civilizations in our Galaxy by utilizing the latest astrophysical information

• Calculations involve:• Galactic star formation histories• Metallicity distributions• The likelihood of stars hosting Earth-like

planets in their habitable zones• Specific assumptions

• The assumptions are based on the one situation in which intelligent, communicative life is known to exist—Earth

• This type of life has developed in a metal-rich environment and has taken roughly 5 Gyr to do so

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• According to the most generous set of assumptions and uncertainty bounds:

• The minimum number of CETI is ∼2900

• With our nearest neighbor at a maximum distance of ∼1880 light years

• Which will require ∼700 yr of SETI to detect

• According to the most limiting set of assumptions and uncertainty bounds:

• The minimum number of CETI is ∼8

• With our nearest neighbor at a maximum distance of ∼50,000 light years

• Which will require ∼6300 yr of SETI to detect

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Looking for Exoplanets – Are We Alone?

• Various studies using various methods reach various conclusions!

• Studies use statistical analyses to estimate the likelihood of intelligent life in the universe• There are lies, damned lies and statistics

• They make use of different assumptions

• Some suggest that intelligent life is common in the universe

• Some suggest that intelligent life is very rare in the universe

• Based on Earth’s history a great number of perhaps unlikely events must occur in series for intelligent life to develop on a planet

• Whether there is intelligent life in the universe we will probably never know for sure

• The universe is BIG and the distances between planetary systems are so large that communication between intelligent life forms is probably not possible • Assumes the current understanding of physics

is correct. i.e. speed of light is limiting

• Radio communication will take years each way• Transmission costs to societies prohibitive

• Travel between star systems could take centuries• Costs and commitment prohibitive

18OLLI Fall 2021

The Truth Is Out There

19OLLI Fall 2021

The Truth Is Out There

Vast distances may preclude our finding it

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