Nov 28, 2016

What Will We Do When Hubble Dies?

For a generation, the Hubble Space Telescope has been exposing the universe's deepest, darkest secrets. From imaging the volcanoes of Jupiter's moon Io, to watching the dramatic breakup of comets, imaging baby galaxies, and helping to nail down the universe's age, its data has been instrumental in today's understanding of the cosmos near and far.

But it's an old telescope, unmaintained since the last space shuttle mission visited in 2009. While the observatory is in excellent health today, it's expected to stop collecting data sometime in the 2020s. What will we lose when the telescope finally dies?

NASA is quick to point out that the James Webb Space Telescope, expected to launch in 2018, will enhance Hubble's capabilities in many ways. But for the telescope's higher resolution and ability to peer back to the very early days of the universe, there is one key thing it doesn't have: ultraviolet capabilities. (It also will lack some of Hubble's fine spectral resolution, and ability to observe a special spectral line called H-alpha that is useful for nebulae and stars.)

Astronomers are being urged to submit as many UV proposals to Hubble as possible because once it dies, there are no immediate plans to launch a successor. (Astronomers could then pull from the archive as needed in future decades.) Earth's atmosphere filters out UV, which is great for protecting life, but bad for UV astronomy, so it needs to be done from space. Astronomers say they don't think another UV telescope will fly until the 2030s, at the earliest.

"For example, one of the big topics that we're going to look at in star and planet formation is the accretion of gas on to young, newly forming stars or planets," said Adam Kraus, an astronomer at the University of Texas at Austin. He explained that as gas falls on to budding stars and planets, they radiate most of their energy in the blue and ultraviolet wavelengths. Webb won't be able to see this as Hubble does, he told Seeker.

The James Webb Space Telescope (pictured here during a mirror inspection) will enhance Hubble's observations in many areas, but it lacks in ultraviolet capabilities.
NASA's Jane Rigby, the deputy project scientist for Webb's operations, points out that the new telescope is designed to do science that Hubble can't. Webb has seven times more collecting area and also works at near absolute zero (the coldest temperature possible). Hubble works at room temperature, so it can't see as well in the infrared. Webb will see into dusty places where stars are forming, or galaxies that have been deeply "redshifted" (with spectral lines moving towards the red end of the spectrum) due to cosmic expansion.

Luckily for astronomers, it's expected that Hubble's and Webb's time in space will overlap. Hubble has a rich archive of observations that Webb could spend time looking at, including the famous "deep fields" of young galaxies. This type of work will be Webb's "bread and butter", Rigby said.

There's also the potential to make stereoscopic or "3D" images of several objects, since Hubble (in low Earth orbit) will be a million miles away from Webb, further out in space. At the Space Telescope Science Institute (STScI), which manages Hubble observations, some astronomers suggest images could be taken of nearby objects.

"You could see Saturn's rings sticking out of the page, Mars looking like a globe, or Jupiter and its moons moving," Joel Green, a project scientist at STScI, told Seeker. "There's a few scientific reasons, too. You might want to look at how cloud structures change in 3D, or how an impact happens in 3D."

Another possibility, he added, would be looking at a star explosion (or supernova) and from the distance between the telescopes, finding out where the explosion is coming from and examining certain features of the explosion.

Hubble's ultraviolet capabilities are not replicated in any telescope now, or in the near future. Here, possible water plumes on Europa (disclosed earlier this year) are imaged using Hubble's ultraviolet filters.
Other observatories are planned after Webb. One is the Wide Field Infrared Survey Telescope (WFIRST), which would use Hubble-class hardware that has a wider field of view. Its specialty would be dark energy and exoplanets. Another is the Transiting Exoplanet Survey Satellite (TESS), which would look at planets passing in front of the brightest stars in our sky. These likely would get going in the 2020s, if funding for the missions is fully approved.

But the next generation is still being worked out. NASA draws heavily from the National Science Foundation's Decadal Survey when planning its missions. Right now, proposals are being formulated to present to members of the next decadal survey, which will be released in 2020.

Read more at Discovery News

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