In 1960, astronomers at West Virginia’s Green Bank Telescope launched the first effort to discover extraterrestrials. Led by Frank Drake, Project Ozma used a radio telescope to detect transmissions at a single frequency of 1420 MHz. This is the frequency emitted by hydrogen clouds and the most common radio emission in the universe. Drake was attempting to receive pulses of transmissions from intelligent life located in star systems Tau Ceti and Epsilon Eridani. More than 50 years later, Frank Drake is still searching for life beyond Earth. Today’s efforts are seeking to increase the coverage and bandwidth of frequencies to find life in the universe.
The first detection of life beyond Earth may not be intelligent life but microbial life in our own Solar System. Where there is water, there may be life. And beyond Earth, there is plenty of water to be found in the Solar System. Mars once had oceans of water on the surface. While the surface is now dry, the subsurface contains significant amounts of water, especially in the high latitudes. The Jovian moons of Europa and Ganymede, along with Saturn’s moon Titan, each have subsurface oceans with more water volume than all of the Earth’s oceans. Missions planned for the next decade may provide evidence for life in these locations.
NASA is developing robotic moles to dig over 600 feet under the Martian surface. These moles will be attached to a tube to send samples to the surface for examination. The Europa Clipper will make repeated flybys of Europa to measure the properties of the subsurface ocean such as salinity. Eventually, plans are to land on Europa and sample the ocean directly. This mission may be 10-20 years off in the future. A key factor in this is planetary protection. If life exists in these locations, missions to detect it have to be sterilized to prevent contamination from Earth’s microbes. To this end, NASA has an office dedicated to this purpose.
Another possibility for life is the Saturn moon Enceladus. This moon ejects water vapor from its subsurface ocean into space. NASA is currently devising instrumentation to study these water samples for a future mission. This would allow for the detection of possible microbial life without the need to burrow into the subsurface saving time and money. Enceladus is pretty young, some estimates are 100 million years old. However, that may be enough time for life to have evolved there.
The environments in the Solar System beyond Earth are too harsh for plant life, but we can use what we know about Earth to detect plant life on exoplanets. Earth’s early atmosphere was mostly carbon dioxide. About 2.7 billion years ago plant life, specifically cyanobacteria, began to convert carbon dioxide to oxygen via photosynthesis. About 2.5 billion years ago, that oxygen began to take hold in the atmosphere. Oxygen is very reactive, that’s why its so combustible, it would not appear naturally in an atmosphere without photosynthesis to produce it as it likes to combine with other elements. If we were able to detect oxygen in sizable quantities in an exoplanet atmosphere, that could be a tell-tell sign plant life exists. This is what is known as a biomarker.
Other biomarkers include methane which is a by-product of living organisms. Both oxygen and methane could be present in an atmosphere naturally. However, if they both appear together, it would most likely be a sign of life. The color of an exoplanet can also serve as a biomarker. Astronomers at Cornell have cataloged 137 microorganisms and the color their pigmentation would reflect if detected on Earth. It is hoped the next generation of 30-40 meter ground telescopes to go online in the next decade, along with the James Webb Space Telescope, will be powerful enough to detect biomarkers.
Of course, most people want to discover more than plant and microbial life, we want to know if there are alien civilizations out there. We typically associate those efforts with the movie Contact and that’s accurate in the sense we listen for radio transmissions from other civilizations. Keep in mind, that will help us discover civilizations just as advanced, or more so, than ours. If an alien race had their radio receivers pointed to Earth from 800-1800 AD, they would not have heard a pique as radio had not been invented yet. Over the past decade, the search for extraterrestrial intelligence (SETI), has received a bump in funding and resources.
In 2001, Paul Allen began to fund the Allen Telescope Array. Rather than scarfing for time on radio telescopes used for other research projects, this array of 42 radio dishes is dedicated solely to SETI. Ultimately the goal is to build 350 dishes and collaborate with similar arrays across the globe. Breakthrough Listen is funded by Yuri Milner. This program will use the Green Bank Radio Telescope, the 64-meter Parkes Radio Telescope in Australia, and the Automated Planet Finder at Lick Observatory. Rather than focus on a single target and frequency, both projects endeavor to survey a million stars across a wide band of frequencies. Besides radio, Breakthrough Listen will also search for optical laser transmissions.
During a recent lecture at Cornell, Frank Drake noted that it had been previously thought lasers could not be transmitted across interstellar distances. New developments in laser technology have changed that. High powered lasers created for controlled fusion research have the capability to reach other stars. The thinking is advanced civilizations might use high powered lasers as a beacon to attempt to communicate across space. The Automated Planet Finder will search for laser signals in this new frontier of SETI research.
When thinking of habitable planets, the Goldilocks Zone is what usually comes to mind. This is the region around a star where water can exist – neither too hot nor too cold. However, other factors come into play in determining a planet’s suitability for life. A magnetic field is required to shield the surface from cosmic rays. An ozone layer is needed to absorb ultraviolet and x-ray radiation that would break apart organic compounds on the surface. A planet’s axis must be moderately tilted and orbit not too elliptical to avoid extreme seasons. Also, the host star should be relatively quiet and not emit flares with excessive radiation. While recent research indicates exoplanets in the Goldilocks Zone are common, they may not necessarily be able to support life.
Looking into the future, the Starshot initiative plans to send probes to our nearest interstellar neighbors to find life. When we think of interstellar voyages, we tend to think big as in Star Trek‘s USS Enterprise which was 947 feet long and held a crew of over 400. Starshot takes the opposite approach. Thinking small, the project aims to design a fleet of nano sized spacecraft. The thinking here is the smaller the mass, the easier to accelerate to velocities required to reach the stars. Also, a fleet of these probes can withstand damage to a few along the way and still complete the mission. New technology needs to be invented to make this a go, but $100 million in funding has started the ball rolling.
In 1961, Frank Drake devised an equation to determine how many intelligent civilizations may exist in the Milky Way. The final term of the equation estimates how long these civilizations last after emitting their first radio signals. We won’t know the answer to this until we start making contact with alien civilizations. Do advanced civilizations destroy themselves? Do natural events such as supervolcanoes disrupt intelligent life? Finding the answers to these questions may help us survive on Earth. May be a bit of a long shot, but most certainly worth making the effort.
*Image atop post is the Allen Telescope Array. Credit: Seth Shostak, SETI Institute.