NEW YORK – A successor to NASA's famous Hubble Space Telescope and the soon-to-be-launched James Webb Space Telescope is already in the planning stages by a group of leading astronomers.
The proposed High Definition Space Telescope, or HDST, would have 25 times the resolution of Hubble and would serve as a "flagship observatory" for the global astronomical community. One of its primary scientific objectives would be to study the atmospheres of dozens of Earth-like alien planets, looking for signs of life.
A new report released Monday (July 6) outlines a broad plan for the telescope. To publicize the report, a panel of scientists involved with the project spoke to the public about the HDST at an event at the American Museum of Natural History (AMNH), here in New York. The event was hosted by Neil deGrasse Tyson, who is director of the museum's Hayden Planetarium. [Celestial Snapshots: Hubble Space Telescope's Latest Cosmic Views]
The report was produced by the Association of Universities for Research in Astronomy (AURA), which is involved with many major telescopes and space science facilities including the James Webb Space Telescope (JWST), the Gemini Observatory and the Space Telescope Science Institute in Baltimore.
The new report gives a launch window for the proposed HDST of sometime in the 2030s. The telescope would view the universe in ultraviolet, optical and infrared light, with a 39-foot-wide (12 meters) multipiece mirror (similar to the honeycomblike mirror on the James Webb Space Telescope). Hubble's primary mirror is 7.8 feet (2.4 m) wide, while that of JWST is 16.4 feet (5.4 m) wide.
Members of the AURA HDST committee said the increase in resolution from Hubble to HDST would be equivalent to the resolution increase from the earliest black-and-white televisions, which had a resolution of about 780 by 420 pixels, to the high-definition screens available today, which are in the range of 3820 by 2160 pixels.
"Bigger telescopes see deeper into space with better detail. Period," Tyson said to reporters prior to the public event. "And it's not just that you will see the objects you already know about better. Our experience tells us that all-new phenomena, undreamt of, manifest themselves in the face of this higher level of technology. And that is what we're actually after here — not simply understanding what we already know a little better. [The HDST has] the potential to make significant, field-changing discoveries."
This sentiment was echoed by Michael Shara, a curator in the department of astrophysics at AMNH, speaking to reporters. Shara explained that in addition to an increase in resolution of images, overall the HDST would be "100 to 1,000 times as powerful as Hubble."
That number comes from combining multiple factors of HDST as they compare with Hubble, including "25 to 35 times the collecting area," or surface area of the telescope (the aperture squared), and four times the area of coverage. AURA's plan for the HDST would place it in a region known as the second Lagrangian point (L2), about 932,000 miles (1.5 million kilometers) from Earth, which would give it a clearer and darker sky than the Earth-orbiting Hubble, reducing background noise from images. (JWST, which is scheduled to launch in 2018, will also orbit at L2.)
"Any time you gain a factor of 100 to 1,000 … you find new astrophysical phenomena," Shara said.
As an example, he and other speakers referenced the accelerating expansion of the universe, caused by what scientists now call dark energy, which was discovered using observations by Hubble but was not predicted by scientists prior to the telescope's launch. The scientists who uncovered the phenomenon were awarded the Nobel Prize in physics in 2011.
A large portion of the AURA report is dedicated to explaining HDST's mission to identify "several dozen" Earth-like planets and analyze their atmospheres for signs of life. HDST's primary search method would involve a coronagraph, an instrument that blocks the light from a star in order to better observe planets orbiting that star.
Sarah Seager, co-chair of the HDST committee and a professor of planetary science and physics at MIT, said no other planned or existing telescope will be able to find anywhere near that many Earth-like planets.
Other telescopes and planet-hunting approaches, including JWST, NASA's Transiting Exoplanet Survey Satellite (TESS), which is scheduled to launch in 2017, and the Wide-Field Infrared Survey Telescope (WFIRST) concept, to name a few, will "have a shot at finding one to a few [Earth-like planets]," Seager said. "But how do you really go forward and find dozens and dozens of them? That's what this telescope is." [7 Ways to Discover Alien Planets]
The HDST would serve many other scientific objectives, the scientists said. Julianne Dalcanton, a professor of astronomy at the University of Washington and co-chair of AURA's HDST committee, said the new telescope would be a "flagship observatory," meaning it would serve a wide range of scientific pursuits, just like Hubble. Scientists around the world would be able to submit proposals for what the telescope should study (this is the case with telescopes like Hubble, but it is in contrast to single-purpose observatories like the Kepler space telescope, which was designed to search only for exoplanets passing in front of their parent stars).
Other potential topics of exploration by the HDST listed in the report encompass nearly all major areas in astronomy. They include studies of large objects like galaxies (both nearby and at the edge of the observable universe) and star-forming gas clouds, as well as studies of planets, moons and other bodies in our own solar system. Dalcanton said the HDST could potentially find planets larger than Earth orbiting the sun in the Kuiper belt or the Oort Cloud, two regions that lie beyond the orbit of Neptune. Other topics of study would include the dawn of galaxy formation in the universe, and star and planet formation in the Milky Way, among others.
In terms of money, Marc Postman, an HDST committee member and an astronomer at the Space Telescope Science Institute, said the cost of the HDST would be "on the order of the James Webb telescope," which he later specified as being between $8 billion and $9 billion.
The committee members also discussed the possibility that human astronauts might service the HDST. Human servicing proved essential to the Hubble Space Telescope when, after reaching orbit in 1990, its primary mirror was found to have been ground to the wrong curvature and it required a corrective attachment. A total of five servicing missions have kept Hubble in operating order and have added upgrades to the telescope. [Photos: NASA's Hubble Space Telescope Servicing Missions]
"I would love to see some astronauts out there at L2," Dalcanton said. "We don't make this a requirement in the report. … The servicing would be fantastic, should the infrastructure come."
Sending astronauts to L2 would be the farthest humans had ever traveled from Earth. During his presentation to the public, Tyson pointed out that astronaut Mike Massimino was in the audience and asked him, "Mike, would you go to L2?" Massimino responded with a quick "Yes."
The panel of scientists said the HDST report was released in anticipation of the 2020 Astronomy and Astrophysics Decadal Survey by the National Research Council of the National Academy of Sciences. The decadal survey is published every 10 years and makes recommendations for projects and pursuits that the global astronomical community should prioritize. The recommendations of the survey often influence which projects and instruments governments and agencies choose to fund.