The Association of Universities for Research in Astronomy (AURA) today released their plans for the High Definition Space Telescope, a futuristic high-definition space observatory the group wants to succeed NASA’s James Webb Space Telescope (JWST). The proposed telescope has a primary mirror that’s nearly 40 feet across — nearly twice the size of JWST. The new proposed telescope should be situated at the second Earth-Sun Lagrange point (L2), an area of space nearly 1 million miles from Earth. Its main goal is to directly image dozens of Earth-like exoplanets throughout our Universe. AURA presented the concept at the American Museum of Natural History this afternoon, through a panel discussion led by Neil deGrasse Tyson.
The space agency has yet to launch the JWST, the successor to the Hubble that will use infrared to look deeper into the Universe than ever before; that telescope will go up some time in 2018. But AURA says it’s time start thinking beyond the JWST. In 1996, AURA wrote a report about what should come after Hubble, and that idea ultimately turned into JWST. Now, they think HDST is the best option for 25 years down the road.
"Are we alone in the Universe?"
The new design is the closest thing we have to a successor for the JWST. Currently, James Webb is considered the next-generation space telescope, surpassing Hubble in scope and ability. It too will sit at the second Earth-Sun Lagrange point — but its goal is more general: to look back in time. The James Webb telescope will use infrared, mostly to observe galaxies that are up to 13 billion light years away. Since the Universe is estimated to be around 13.8 billion years old, the light seen from these galaxies will be from when they were very young or just forming, allowing us to get a glimpse of the dawn of the early cosmos.
AURA is in favor of JWST. But the group also says astrophysicists are in need of a different kind of telescope with a more focused goal. The group, in a statement, argues that despite how much our species has discovered, we still don't have the answers to some of our biggest questions: "Are we alone in the Universe? Are other Earth-like worlds common? Do any have signs of life? How did life emerge from a lifeless cosmic beginning?" AURA says with the right telescope, we can finally resolve these queries.
That's where the HDST comes in. After launch, the scope will directly image exoplanets orbiting around hundreds of stars. That’s similar to the goal of the Kepler mission, a space observatory launched by NASA to discover Earth-like planets orbiting other stars in the Milky Way Galaxy. Right now, thanks to Kepler and other Earth-based observations, we’ve found nearly 2,000 exoplanets in our Universe. Most of them haven’t been seen directly, but astronomers estimate that there are around 11 billion Earth-size planets orbiting Sun-like stars in the coveted "habitable zones" — regions around stars in which planets can support liquid water — in the Milky Way Galaxy alone.
So AURA wants a better telescope to peek at these worlds — hence HDST, which is, essentially, the James Webb telescope but with a Kepler mission. Unlike Kepler, HDST is designed to image exoplanets directly. Right now, we rely on indirect imaging methods to catalog exoplanets — such as observing the periodic dimming that occurs when exoplanets cross in front of their host stars. The proposed HDST improves on that. It may be able to observe the dim light the planets throw off directly, using wavelengths ranging from ultraviolet to near-infrared. That means the observatory will be able to directly characterize a planet's atmosphere — an important feature that will help determine whether or not these space rocks house life. With a big enough sample of planetary atmospheres, AURA argues it will be much more possible to observe the "telltale" signs of life.
The observatory will be able to directly characterize a planet's atmosphere
"If life is rare, HDST will take us from our current complete ignorance of the occurrence rate of inhabited worlds to a first constraint, potentially showing how remarkable our own existence is," AURA writes. "If life is common, a large sample of terrestrial worlds with highly unusual atmospheric chemistry will secure our belief that life of some kind exists beyond the Earth, regardless of possible false positives."
Some of the technology needed to turn HDST into reality isn't ready. In order to accurately capture an exoplanet's atmosphere, astronomers will need an as-yet undeveloped technique known as starlight suppression. Many of these worlds orbit incredibly bright stars that engulf the exoplanets in light, making them extremely hard to see; some exoplanets are about 10 billion times fainter than their host stars. Starlight suppression, in theory, would block out starlight to one part per 10 billion to allow for direct detection of orbiting planets. Today’s announcement is a kind of heads up to physicists to develop the technology to make the HDST telescope possible.
Since the Kepler mission, we’ve known there are other Earthlike planets in the habitable zone, but the indirect methods of observation make it hard to puzzle out what atmospheres — if any — surround these planets. If we want to know for sure which planets may be our best hopes for finding out whether we’re alone out here, we’ll need to look at these worlds directly. With proper funding, HDST could give us our best look yet.
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