Only a small fraction of space has been searched for aliens | Science News for Students

Only a small fraction of space has been searched for aliens

How little? A volume equivalent to a hot tub’s worth of the Earth’s oceans
Oct 24, 2018 — 6:45 am EST
a photo of the Arecibo radio telescope from the air

The Arecibo radio telescope in Puerto Rico (here) has been used for decades in the search for extraterrestrial intelligence (SETI). But these efforts have searched only a very tiny portion of the skies, new calculations suggest.

Courtesy NAIC-Arecibo Observatory, an NSF facility

Scientists have been searching for signals of aliens for 60 years. So far, they’ve had no luck in finding any. So you’d be forgiven for thinking, “Where is everyone?”

In fact, the lack of success may just reflect not looking widely enough.

A new calculation shows that if space is an ocean, we’ve barely dipped in a toe. The volume of observable space combed so far for E.T. is comparable to searching a volume the size of a large hot tub for evidence of fish in Earth’s oceans. That’s according to Jason Wright and his colleagues. Wright is an astronomer at Pennsylvania State University in University Park. His team presented its calculations in a paper posted online September 19 at

“If you looked at a random hot tub’s worth of water in the ocean, you wouldn’t always expect a fish,” Wright says.

Still, that’s far more space searched than had been calculated back in 2010. That estimate had been done for the 50th anniversary of the search for extraterrestrial intelligence, or SETI.

SETI programs have searched for messages from aliens in radio waves. This is the same range of frequencies over which music and news are sent to your car. But it’s also the range that scientists think is easiest to monitor for communication from across the universe.

In the 2010 work, SETI pioneer Jill Tarter and her colleagues imagined a “cosmic haystack.” It was made not of hay, but of naturally occurring radio waves. The researchers considered what it would be like to sift through that haystack for the proverbial needle. That needle would be an artificial, alien beacon. Her haystack went beyond physical space. It also included factors such as a possible signal’s duration, frequency, variations and strength. And it accounted for the sensitivity of radio telescopes on Earth that would attempt to detect a signal.

Tarter’s group concluded that searches had covered about a drinking glass’s worth of seawater. That would hardly be enough to conclude an ocean is fishless.

Wright worked with his colleagues Shubham Kanodia and Emily Lubar to update Tarter’s calculation. They devised a slightly different haystack. It included factors like the frequency and bandwidth aliens might broadcast in. It also included more recent SETI searches such as the Breakthrough Listen project. It’s the largest project yet to search for signs of alien life.

The researchers converted the volume of space to liters of ocean for the sake of analogy. And SETI has covered the equivalent of 7,700 liters out of 1.335 billion trillion liters of water in Earth’s oceans, they now conclude. That’s like taking a hot-tub’s worth of water out of the ocean. You might find a fish in there, but if you don’t, it would not be all that surprising.

“We’re finally getting to the point today … that we have a chance of finding something, depending on how much there is to find,” Wright says. So there’s no point in giving up the search yet.

Power Words

(more about Power Words)

alien     A non-native organism. (in astronomy) Life on or from a distant world.

arXiv     A website that posts research papers — often before they are formally published — in the fields of physics, mathematics, computer science, quantitative biology, quantitative finance and statistics. Anyone can read a posted paper at no charge.

astronomy     The area of science that deals with celestial objects, space and the physical universe. People who work in this field are called astronomers.

broadcast     To cast — or send out — something over a relatively large distance. A farmer may broadcast seeds by flinging them by hand over a large area. A loudspeaker may send sounds out over a great distance. An electronic transmitter may emit electromagnetic signals over the air to a distant radio, television or other receiving device. And a newscaster can broadcast details of events to listeners across a large area, even the world.

colleague     Someone who works with another; a co-worker or team member.

cosmic     An adjective that refers to the cosmos — the universe and everything within it.

E.T.     (n.) An abbreviation made famous by the 1982 Universal Pictures movie, E.T. the Extra-Terrestrial. The main character was a charming space alien called E.T. His most famous line from the movie was “E.T. phone home.” E.T. has since come to be used as a colloquial term for any intelligent and potentially friendly space alien.

extraterrestrial     (ET) Anything of or from regions beyond Earth.

factor     Something that plays a role in a particular condition or event; a contributor.

frequency     The number of times a specified periodic phenomenon occurs within a specified time interval. (In physics) The number of wavelengths that occurs over a particular interval of time.

physical     (adj.) A term for things that exist in the real world, as opposed to in memories or the imagination. It can also refer to properties of materials that are due to their size and non-chemical interactions (such as when one block slams with force into another).

radio waves     Waves in a part of the electromagnetic spectrum. They are a type that people now use for long-distance communication. Longer than the waves of visible light, radio waves are used to transmit radio and television signals. They also are used in radar.

random     Something that occurs haphazardly or without reason, based on no intention or purpose.

range     The full extent or distribution of something. For instance, a plant or animal’s range is the area over which it naturally exists. (in math or for measurements) The extent to which variation in values is possible. Also, the distance within which something can be reached or perceived.

seawater     The salty water found in oceans.

SETI     An abbreviation for “search for extraterrestrial intelligence,” meaning life on other worlds.

telescope     Usually a light-collecting instrument that makes distant objects appear nearer through the use of lenses or a combination of curved mirrors and lenses. Some, however, collect radio emissions (energy from a different portion of the electromagnetic spectrum) through a network of antennas.

trillion     A number representing a million million — or 1,000,000,000,000 — of something.

universe     The entire cosmos: All things that exist throughout space and time. It has been expanding since its formation during an event known as the Big Bang, some 13.8 billion years ago (give or take a few hundred million years).

wave     A disturbance or variation that travels through space and matter in a regular, oscillating fashion.


Journal:​ J.T. Wright, S. Kanodia and E. Lubar. How much SETI has been done? Finding needles in the n-dimensional cosmic haystack. arXiv:1809.07252v1. Posted September 19, 2018.

Journal:​ J.C. Tarter et al. SETI turns 50: five decades of progress in the search for extraterrestrial intelligence. Proceedings of SPIE, Volume 7819, Instruments, Methods, and Missions for Astrobiology XIII. Published online September 7, 2010. doi: 10.1117/12.863128.