Carnegie Astronomer Visits the Optimists

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The Milky Way is only one of trillions of galaxies in space.

When Dr. John Mulchaey addressed “Exploring Life in the Universe” at an Optimist Club meeting on Zoom in June, he was asked, “Are there other civilizations out there?”

Mulchaey, director of the Carnegie Observatories, said there is probably “life in hundreds of thousands of planets in the universe.”

He said that astronomers make several assumptions to come to that conclusion. The first one is to determine how many planets there are in the universe.

“Our technology is only good enough that we can research 300 light-years from the sun,” he said. “There are about 200 billion stars in the Milky Way and about one trillion planets.”

If there are about 10 trillion galaxies, then the total number of planets could be 10 trillion times one trillion, which means there “are about a million times more planets than grains of sand on earth,” Mulchaey commented.

After determining the possible number of planets, scientists then look for planets with life. “There are three ways we do that,” said Mulchaey, who investigates groups and clusters of galaxies and is the scientific editor for The Astrophysical Journal.

They look for communications that would target Earth’s radio and telescopes, but he concludes “that any detectable signal from aliens would likely need to be directed at earth,” which would make this method difficult.

A second method would be to look at planets that might have a bio-signature in the atmosphere, which means they would have water, nitrogen, carbon dioxide or hydrogen.

“Oxygen and ozone come from photosynthesis,” Muchaey explained, noting “our own atmosphere has signatures of life.”

Mulchaey said that an exoplanet atmosphere telescope, the Giant Magellan Telescope (visit:, which is being constructed in Chile, will have resolving power 10 times greater than the Hubble Space Telescope. Astronomers hope that when this telescope is online, it will help answer, “Are we alone in the universe?”

(Editor’s note: The telescope will be located in one of the highest and driest regions on earth, Chile’s Atacama Desert, and have spectacular conditions for more than 300 nights a year. Las Campanas Peak, where the GMT will be located, has an altitude of about 8,500 feet. The site is almost completely barren of vegetation due to lack of rainfall, making this an ideal location for the GMT.)

The third place scientists are looking for life “is elsewhere in this solar system.”

Scientists are looking on Mars and “maybe early in that planet’s life there was life,” Mulchaey said. “Maybe we’ll find fossilized life.”

He said that on Jupiter’s moons, Europa and Ganymede, and Saturn’s moon Encladus, that “We know there are geysers and that there are oceans under them. It would be a great place to find life.”

He also said scientists are interested in Triton, another Saturn moon, covered by a thick atmosphere.

Mulchaey said another enigma is Venus. Although the surface temperature is about 870 degrees Fahrenheit, there is phosphine in the upper atmosphere and phosphine is associated with bacteria.

“Are we alone in the universe?” he asked and then predicted, “We’ll know the answer in the next few decades.”

He was asked if he believed in UFO’s. “I’m skeptical,” he said. “No astronomers have seen them. For aliens to have visited the earth, the technology would have to be impressive.”

Another Optimist asked, “If you go out into space forever – is there an end?”

Mulchaey responded, “There is no end to the universe. Space doesn’t have boundaries or edges and space is increasing in size.”

For those who are worried about the end of the Earth, Mulchaey said that the sun should be stable for about another four and half billion years. “The sun is about halfway through its lifetime,” he said.

Another Optimist asked, “What are the chances the earth will be hit by an asteroid, like one that most possibly wiped out the dinosaurs?”

“More recently there’s less ‘stuff’ in the atmosphere,” the astronomer said, noting that this makes that scenario less likely. He also noted that even if the earth were hit, “Life is resilient.” But he warned, “We’re the most likely to destroy the earth.”

He was once again pressed about UFO’s and the suspicion that there could have been a government cover-up at some point. Mulchaey tends to think a secret like that would have leaked out by now. “I like to have data,” he said.

Mulchaey received his B.S. in astrophysics from UC Berkeley and his Ph.D. from the University of Maryland. He was a fellow at the Space Telescope Science Institute and at Carnegie before joining the Carnegie.

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2 Responses to Carnegie Astronomer Visits the Optimists

  1. Lee Calvert says:

    Sue my great grandson is very interested (he’s 18) in this kind of thing – any way I can send this article to him? He just graduated high school … Thanks, Lee

  2. Sue says:


    Please share it with him–or you can just sent him a link and he can read it directly off the site.


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