ASTRO 200/200G - Astrobiology Lecture 20: Search for Extraterrestrial Intelligence

Instructor: Professor Kathy Campbell
Institution: The University of Auckland, Te Whare Wānanga o Tāmaki Makaurau, New Zealand
Focus of Lecture: Search for Extraterrestrial Intelligence (SETI)

Many astronomers believe that finding extraterrestrial life is a matter of time rather than possibility.
Key Points:
- Optimism about detecting life signs in the next few years.
- Mention of the potential for life in icy moons of Jupiter.
- NASA's James Webb Space Telescope (JWST) detected signs of life on a distant exoplanet (K2-18b).
Quote from Prof. Catherine Heymans:
- "We live in an infinite Universe, with infinite stars and planets. And it’s been obvious to many of us that we can’t be the only intelligent life out there."
- Technological advancements now allow us to seek answers about our existence in the cosmos.

The JWST possibly detected a molecule, dimethyl sulphide (DMS), potentially indicating life on K2-18b (120 light years away).
- DMS is predominantly produced by life on Earth, primarily through phytoplankton.
- Other detected gases: methane and CO2, which suggest the presence of a water ocean.
- Quote by Prof. Nikku Madhusudhan: "On Earth, DMS is only produced by life."

SETI seeks to answer whether we are alone in the Universe.
Interest in the electrical and optical frequencies as potential carriers of extraterrestrial signals.
Begins hypothesizing about intelligent extraterrestrial life making contact via signals.
Importance in addressing fundamental human questions about existence and extraterrestrial life.

Timeline of SETI:
- 60 years ago, interest in signals from space began.
- Project Ozma (1960): First significant attempt to detect signals, lead by Frank Drake, monitoring Tau Ceti and Epsilon Eridani for 150 hours.
- SERENDIP (Search for Extraterrestrial Radio Emissions from Nearby Developed Intelligent Populations): Initiated by UC Berkeley.
Modern SETI projects utilize spare time on radio telescopes and collective processing through BOINC (Berkeley Online Infrastructure for Network Computing).

1420 MHz Frequency:
- Hydrogren atom emissions (1 proton, 1 electron) are suggested as a likely signal frequency due to their abundance in the Universe.
- Close by, 1640 MHz for hydroxyl radical (OH-) emissions is noted as a potential signal pathway, suggesting that civilizations might congregate around this "water hole" in space.
- Significance of detectable frequencies supported by Earth’s transparent atmosphere.

Detected on 15 August 1977 at 1420 MHz by the Ohio State University's Big Ear telescope, it was a strong, narrow-band radio signal lasting 72 seconds.
For 40 years, it was the most promising candidate for extraterrestrial communication; later speculated to be caused by a passing comet (termed a "false positive").

Breakthrough Listen Initiative: Initiated with a $100M donation to enhance search capabilities for extraterrestrial intelligence.
Hypothesis: Accessing more areas increases the likelihood of discovering proof of extraterrestrial life.
Estimates of potential civilizations:
- One in a million of the 1 trillion planets in the Milky Way could harbor intelligent life.

Records of Observations (2019):
- Analysis of 1,300 star systems over 3 years with zero significant findings.
- Plans to expand searches to 1 million star systems.

Method focusing on light signals that could be transmitted via powerful lasers, which might be far more efficient than radio signals.
Example of human lasers being 5000 times brighter than the Sun.
Challenges include noise issues in the optical spectrum, encouraging exploration of infrared SETI methods.

Formulated by Frank Drake in 1961, used to estimate the number of extraterrestrial civilizations.
Components of the equation:
- $N = R^* \times f<em>p \times n</em>e \times f<em>l \times f</em>i \times f_c \times L$
- N: Number of civilizations with detectable transmissions.
- Parameters Defined:
  - $R^*$ = Rate of star formation suitable for intelligence (annual).
  - $f_p$ = Fraction of those stars with planetary systems.
  - $n_e$ = Number of planets per star that could support life.
  - $f_l$ = Fraction of suitable planets where life appears.
  - $f_i$ = Fraction of planets with life that become intelligent.
  - $f_c$ = Fraction of civilizations that develop communication.
  - $L$ = Length of time civilizations can communicate.
Estimates range drastically, with some suggesting millions of civilizations could exist in the Milky Way Galaxy.

Enrico Fermi questioned the apparent contradiction between high estimates of extraterrestrial civilizations and the lack of evidence for or contact with such civilizations.
Numerous hypotheses attempt to resolve the paradox:
- Civilizations are too far apart,
- Very few civilizations exist,
- Self-destruction of intelligent life,
- Periodic natural destruction of civilizations,
- Misperceptions of contact possibilities.

A method of measuring a civilization's energy consumption:
1. Type I Civilization: Utilizes all available resources on its home planet (approx. $10^{12}$ Watts).
2. Type II Civilization: Harnesses energy from its star (approx. $10^{26}$ Watts).
3. Type III Civilization: Manages energy from an entire galaxy (approx. $10^{37}$ Watts).
Most atomic-scale civilizations are not classified as Type I yet, indicating humanity's emerging status.

Einstein's relativity limits travel speed to below light speed. Traveling to Proxima Centauri (4.26 light years) at light speed would take over 8 years.
Future propulsion technologies:
- Nuclear fission and fusion as energy sources for rockets.
- Ion drives and solar sails as potential methods for reaching significant speeds overtime.

Questions arise about representation and coordination with extraterrestrial beings, including who should speak for humanity.

Although no confirmed signals have been detected, the increased capability and theoretical framework supports a hopeful future in the quest for alien communication.