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


Support nonprofit journalism

Subscribe now


We may not have found aliens yet because we’ve barely begun looking

A new calculation compares the effort so far to exploring a hot tub’s–worth of Earth’s oceans

8:00am, September 30, 2018
Arecibo radio telescope

IS ANYBODY OUT THERE?  The Arecibo radio telescope in Puerto Rico has been used for decades in the search for extraterrestrial intelligence (SETI) but has barely made a dent in the space to be searched, new calculations suggest.

Sponsor Message

With no luck so far in a six-decade search for signals from aliens, you’d be forgiven for thinking, “Where is everyone?”

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 the volume of a large hot tub for evidence of fish in Earth’s oceans, astronomer Jason Wright at Penn State and colleagues say 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 calculated in 2010 for the 50th anniversary of the search for extraterrestrial intelligence, or SETI. In that work, SETI pioneer Jill Tarter and colleagues imagined a “cosmic haystack” of naturally occurring radio waves she could sift through for the proverbial needle of an artificial, alien beacon (SN Online: 5/29/12). Her haystack went beyond physical space to include factors such as a possible signal’s duration, frequency, variations and strength, as well as the sensitivity of radio telescopes on Earth that would presumably detect a signal.

She concluded that searches had covered about a drinking glass’s worth of seawater — hardly enough to conclude the ocean is fishless.

Wright and colleagues Shubham Kanodia and Emily Lubar updated Tarter’s calculation by devising a slightly different haystack, including factors like the frequency and bandwidth aliens might broadcast in. It also included more recent SETI searches such as the Breakthrough Listen project (SN Online: 7/20/15).

Converting the volume to liters for the sake of analogy, the researchers concluded that SETI has covered the equivalent of 7,700 liters out of 1.335 billion trillion liters of water in Earth’s oceans.

“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.


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.

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 September 7, 2010. Doi:10.1117/12.863128

Further Reading

L. Grossman. We probably won’t hear from aliens. But by the time we do, they’ll be dead. Science News. Vol. 193, April 14, 2018, p. 9.

C. Crockett. Search for E.T. gets financial boost. Science News Online, July 20, 2015.

N. Drake. An interview with alien hunter Jill Tarter. Science News Online, May 29, 2012.

N. Drake. The Drake Equation turns 50: An interview with Frank Drake. Science News Online, November 1, 2009.

Get Science News headlines by e-mail.

More on Rosetta

From the Nature Index Paid Content