The RATAN-600 radio telescope in Zelenchukskaya Mikhail Turnovskiy/Alamy Stock Photo

Are you there, ET? Recent news of a spike in radio signals that could fit the profile for an intelligent, extraterrestrial source has SETI astronomers across the globe swinging their radio dishes in hopes of confirming the detection. Although so far they have all come back empty-handed, two observatories will follow up on the tantalising signal again tonight.

The signal was detected on May 15, 2015 by a radio telescope operated by the Russian Academy of Science. It appeared to come from the star HD 164595, a sun-like star located roughly 95 light-years from Earth. The system has only one known planet: a warm Neptune, so called because it is gaseous like Neptune but orbits its star in only 40 days. But the star probably has other planets — perhaps rocky ones — as well.

The researchers speculate that such a bright signal, if real, could have been produced by a radio beacon built by an intelligent civilisation.

If that beacon is transmitting radio waves in all directions, the energy it would need to produce is a whopping 1020 watts, says Seth Shostak, an astronomer at the SETI Institute in California. “That’s a big energy bill even if you’re getting a bulk discount from your local supplier,” he jokes. “It’s hundreds of times more than all the energy falling on the Earth from sunlight.”

That means the hypothetical beings responsible might be what SETI scientists call a Kardashev Type II civilisation, so advanced that they can tap all of the energy being produced by their host star.

If instead the beacon was targeted at Earth, then the power needed drops to 1013 watts, Shostak says. “That is more or less the total amount of energy used by humankind — all the cars, all the planes, all the electronic devices, everything,” Shostak says. “This is not a high-school science project.”

That would make the senders a Kardashev Type I civilisation, able to harness all the starlight that falls on its home planet.

Jumping to conclusions?

Although it’s fun to speculate, it’s far more likely that the signal isn’t an extraterrestrial beacon at all, but actually earthly interference. Radio telescopes have been known to pick up rogue signals – everything from flushing toilets to cell phones. Just last year, astronomers at the Parkes Radio Telescope in Australia traced a mysterious type of radio signal to two on-site microwave ovens.

“In SETI part of the problem is that you have a civilisation that is producing signals that can mess you up all the time – and that civilisation is called humanity,” Shostak says.

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So before astronomers jump to any conclusion, they’re attempting to detect the signal again. Last night, the SETI Institute used the Allen Telescope Array in northern California to track the star. They saw nothing, but will observe again tonight.

That lack of detection doesn’t close the book on an extraterrestrial civilisation just yet. “You can’t say because you didn’t find something that there’s nothing there,” Shostak says. “Say Captain Cook sailed around all day in the South Pacific and he didn’t find any new islands. That doesn’t prove that there are no new islands, it just proves that he didn’t find any that day.”

A civilisation might also try to send signals at multiple frequencies, says Douglas Vakoch, the president of METI International, a group that wants to send messages to ET as well as detect their signals. Perhaps last night, they simply weren’t broadcasting at the same frequency we initially detected.

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“If you really want to communicate a lot of information there are advantages to sending at optical frequencies,” he says. “So we are planning to observe the star from our optical SETI observatory in Panama this evening. We tried last night but the weather didn’t cooperate.”

Still, Vakoch is not particularly optimistic that they will find anything. “I think the likely outcome of this is that there’s no indication that it’s ET, but it provides a critical preparation for a day we may really discover intelligence out there,” he says. “We can speculate as much as we want about whether there’s intelligence out there in the cosmos, but unless we find something interesting and do a rigorous follow-up, we’ll never know.”

An earlier version of this story misstated the distance to the star. This has been corrected.