Astronomers want NASA to build a giant space telescope to peer at alien Earths

NASA should work towards building a giant new space telescope that's optimized for getting images of potentially habitable worlds around distant stars, to see if any of them could possibly be home to alien life.

That's according to a new report from the National Academies of Sciences, Engineering, and Medicine. Every ten years, at the request of government science agencies including NASA, this independent group of advisors reviews the field of astronomy and lays out the top research priorities going forward.

"The most amazing scientific opportunity ahead of us in the coming decades is the possibility that we can find life on another planet orbiting a star in our galactic neighborhood," says Fiona Harrison, an astrophysicist at Caltech who co-chaired the committee that wrote the report.

"In the last decade, we've uncovered thousands of planets around other stars," says Harrison, including rocky planets that orbit stars in the so called "Goldilocks Zone" where temperatures are not too hot and not too cold for liquid water and possibly life.

That's why the expert panel's "top recommendation for a mission," says Harrison, was a telescope significantly larger than the Hubble Space Telescope that would be capable of blocking out a star's bright light in order to capture the much dimmer light coming from a small orbiting planet.

A just-right telescope for 'Goldilocks Zone' planets

Such a telescope would be able gather infrared, optical, and ultraviolet wavelengths, in order to observe a planet that's 10 billion times fainter than its star and learn about the make-up of its atmosphere, to search for combinations of gases that might indicate life. This telescope would cost an estimated $11 billion, and could launch in the early 2040's.

The panel did consider two proposals, called HabEx and LUVOIR, that focused on planets around far-off stars, but ultimately decided that LUVOIR was too ambitious and HabEx wasn't ambitious enough, says Harrison. "We decided that what would be right is something in between the two."

These kinds of recommendations, which are produced with help and input from hundreds of astronomers, carry serious weight with Congress and government officials. Previous "decadal surveys" endorsed efforts that ultimately became NASA's Hubble Space Telescope as well as the James Webb Space Telescope, which is scheduled to launch December 18.

The James Webb Space Telescope, however, ran years behind schedule and billions of dollars over budget — and astronomers want to avoid a repeat of that experience. "We kind of came up with a new way of evaluating and developing missions," says Harrison.

'There is no one winner'

Other top research priorities identified by the group include understanding black holes and neutron stars, plus the origin and evolution of galaxies.

The panel recommended that sometime in the middle of this decade, NASA should start work towards two more space telescopes: a very high resolution X-ray mission and a far-infrared mission. The panel considered a couple of designs, called Lynx and Origins, but ultimately felt that less costly instruments, in the range of $3 billion or $4 billion, would be more appropriate.

"When we looked at the large projects that came before us, we were really excited by all of them," says Rachel Osten, an astronomer with the Space Telescope Science Institute who served on the expert committee. "We appreciate all the work that went into getting them to the stage that they were at."

But all of them were still very early concepts, says Osten, and because more study needs to be done to understand the costs and technologies, "what we have done is identify what our top priorities are both on the ground and in space," rather than ranking mission proposals or adopting a winner-take-all approach.

"There is no one winner," she says. "I think everyone wins with this."

After all, Osten says, 20 years ago, researchers barely knew of any planets outside of our solar system, and now astronomers have advanced their science to a point where "we have a route to being able to start to answer the question, Are we alone?"