Space Astronomy After the Great Observatories
Eric P. Smith
James Webb Space Telescope Program Scientist
About the Lecture
For the last decade the NASA Great Observatories, The Hubble Space Telescope, Compton Gamma-ray Observatory, Chandra X-ray Observatory and the Spizter Space Telescope have driven many astronomy advances. These instruments conceived initially in the 1970s, but formalized as a program in the 1980s, have expanded our understanding of the cosmos. New celestial phenomena like the accelerating universe, gamma ray bursts, and extrasolar planets investigated by these missions have deepened our astronomical understanding and sense of mystery simultaneously. Surely, to quote from nearly every scientific paper, “more data will be required”. But where and how will space astronomy and astrophysics advance after these facilities are only textbook lessons? Does this grand assembly of telescopes represent NASA’s “Astronomy Apollo Program”, mythic in its accomplishments, possibly never to be duplicated? This lecture will cover some of the science questions that promise to drive astronomy in the coming years and perhaps decades. With these as starting points the lecture will go into NASA’s plans for new observatories both near and longer term. The lecture will also discuss subsequent generations of telescopes to further our understanding of the universe.
About the Speaker
ERIC P. SMITH is the James Webb Space Telescope and Hubble Space Telescope Program Scientist at NASA Headquarters, Washington, D.C. He’s the senior NASA scientist responsible for the Webb science content and is also responsible for monitoring and managing the science program for both the Webb Telescope and Hubble. He defines and safeguards the “Level 1” science requirements for Webb. These delineate the essential capabilities the observatory must possess such as primary mirror size, instrument complement, and mission lifetime. He works with the Webb Project Science Team and the Science Working Group during the observatory’s development to see that the developing hardware measures up against the science requirements. Before coming to NASA Headquarters he worked at the Goddard Space Flight Center on the science team for the Space Shuttle borne Ultraviolet Imaging Telescope, and on the data archiving and distribution system for Hubble He holds a B.A. in Physics and Astronomy from the University of Virginia and a M.S. and Ph.D. in Astronomy from the University of Maryland, College Park.
President Robin Taylor called the 2,264th meeting to order at 8:16 pm January 22, 2010 in the Powell Auditorium of the Cosmos Club. The minutes of the 2,262nd meeting were read and approved.
Ms. Taylor introduced the speaker of the evening, Mr. Eric P. Smith of NASA. Mr. Smith spoke on “Space Astronomy After the Great Observatories.”
Mr. Smith spoke briefly of Galileo’s interest in the sky and outlined what was known then. In the 20th century, military needs increased interest in the heavens. After WWII, interest in other than visible parts of the spectrum grew. In the late 1970's and early 1980's, they planned how to pursue the interest.
The fun-loving NASA folks of that time illustrated their plans with a cartoon book, which Mr. Smith used to illustrate his lecture. Five parts of the spectrum were targeted. A radio-telescope was included, but it was ground based. The four space facilities were the Gamma-ray Observatory, the X-ray Observatory, later to be called Chandra, the Spitzer Space Infrared Observatory, and the Hubble. The idea was to cover the spectrum, assuming that, if you looked at a galaxy with all of them, you would be probing different parts of it with each observatory.
The great observatories became reality. Hubble was launched 20 years ago this year. The Hubble serves the largest constituency because people have been studying light for centuries. The Compton Gamma-ray Observatory was launched second, in 1991. He showed the Chandra X-ray Observatory. Chandra has an unusual elliptical orbit that reaches very high. The last one was the Spitzer, which works on infrared light.
The Space Shuttle was a major factor in the design of these observatories. The Spitzer was launched after the Shuttle accident, using a Delta Rocket. Although reduced from a 4-meter aperture to 85 cm, it has still made amazing discoveries, because it was the first infrared observatory in space. Mr. Smith believes the Shuttle period was a unique time for NASA and it may not occur again.
He showed a series of pictures of a galaxy taken by the different observatories. They show different things, since they each receive radiation produced at different temperatures. Gasses from 10,000°C to 100°C are sensed. He showed a picture compiled from all four, except for the Compton Gamma-ray data, which would have been a point at the center.
He told of the great discoveries enabled by the Great Observatories. The greatest one, he said, was the discovery of dark energy and the related discovery that the expansion of the universe is accelerating, not decelerating. The key element of this was the ability of Hubble to accurately receive usable light from supernovae in distant galaxies, measure their distances, and map their spectra.
The existence of dark matter was actually posited in the 1940's or 1950's, when Vera Rubin showed that there is matter in galaxies that is not emitting light. What the Hubble and Chandra did was to elucidate the matter on a large scale. A few years ago, coordinated Hubble and Chandra observations of a collision of two giant clusters of galaxies showed that the gas emitted is not coincident with the stars. The gas was actually following the dark matter. This was “pretty much the definitive proof” of the existence of dark matter, Mr. Smith said.
Even before Chandra, the diffuse X-ray background was known. The resolution of Chandra enabled the discovery of where that X-radiation comes from, the black holes at the centers of galaxies. Chandra shows how black holes sculpt and carve out the environment near galaxy centers.
A recent discovery, from Spitzer, was the dust rings around planets. Compton discovered a unique type of Gamma-ray burst and a distinct class of active galaxies, called Blazars, which emit most of their energy as Gamma-rays.
Mr. Smith noted that his grandmother, who is 93, is older than galaxies. When she was born, people did not know that galaxies existed as a distinct phenomenon. With the James Webb Space Telescope, he said, we hope “to complete the history of galaxies.”
He showed some counts of stories from Science Magazine. In the ten to 20 years since the Great Observatories were launched, they have exceeded the number of stories from NASA from all other sources.
That’s the very successful history. Three of the Great Observatories are still working today. Chandra is working as designed. Spitzer still has two instruments working, although one was cryogenic and its cryogens have run out, so only one is still working as planned. The Hubble was serviced in May and is working better than ever.
What next? A next generation of great observatories? That would be logical, but they were developed at that unique time, of the Shuttle. A shuttle is now viewed as a very costly way to get science data.
There are 14 satellites returning data right now, and another will become operational this year. More data are coming than ever.
One of them is the Fermi Gamma-ray Observatory. It has been in orbit about a year. It has been discovering specific types of pulsars.
While astronomers like high-energy phenomena, what excites the public are planets. The Keppler Satellite is designed to answer the question: How many earths are there in a galaxy? To do this, it takes one view of space and monitors the brightness of 140,000 stars simultaneously, every few seconds. When planets pass, the brightness dips. The data from Keppler don’t tell us much yet, since they have to establish the timing of the brightness dips to infer that they are caused by planets.
The Keppler is different from the Great Observatories, since it constantly gauges a single field. Mr. Smith calls it an experiment.
The next step in great observatories is best represented by the James Webb Space Telescope. It looks different. It has a 6.5 meter mirror. It has cameras and spectrographs. Unlike Hubble, it reads infrared, not visible light. It can see farther, so it sees galaxies that were created earlier. It will be in orbit 1.5 million km from earth, four times as far as the moon. The moon, the earth, and the sun will all be in one direction, so they will be able to block light with a small shield.
Another thing on the drawing board is a telescope that would be so large it would have to unfold in space. It would be the next step, a marriage between the Hubble and Spitzer. It would be the scientific successor.
There are plans for an international X-ray observatory. It will have scientific foci like those for Chandra, but will be able to see deeper into space. It will have much higher resolution.
Another possibility is something that might be called a laser interferometry space antenna. It would be a series of three satellites which would measure the distance to each other by lasers. Each one would be 5 million km from each other. The purpose would be to watch for subtle ripples in the fabric of space-time, gravitational waves. It would open a third way to get information from space. At present all we have from space are photons and particles.
Then, there is the possibility of a larger version of Hubble. They are looking at possibilities of mirrors in the range of 8 to 16 meters.
Speculating on what the future holds, he said he hopes the field does not get captured by the image of reinventing the Apollo. That kind of funding increase could not be repeated. He hopes astronomers will be able to benefit from the smaller, specialized observatories the future is likely to hold and he hopes there will be more than four observatories.
Mr. Smith agreed to answer questions.
If you got a 50% increase in funding, what would you do? We take guidance, he said, from the astronomer community. I would wait until next September, when we have our next conference of the community. I would initiate the development of one of the bigger observatories and try to get the smaller ones back on a more regular launch basis.
Another question was about seeing objects in the sky that might hit Earth. Mr. Smith told about a satellite called WISE, Wide-field Infrared Survey Explorer, which was launched December 9. Its original purpose was to find infrared phenomena, but they changed it to survey scan the territory twice so it can identify things that are moving.
Another question was about whether changes in the temperatures on Mars and Venus are coincident with the changes on Earth. Mr. Smith said most of the satellites can’t look at planets with orbits smaller than Earth’s. Existing observations have not produced much information on this.
Someone asked if gravitational waves might enable us to see closer to the Big Bang than 300 thousand years after it. Yes, they might. Gravitational signatures imparted by the Big Bang might be found. There is also a possibility of using balloons to look at gravitational waves and cosmic radiation.
About proposed heavy lift launch vehicles, he said none of them reduce the cost to payload ratio much, so he does not expect them to be built. They would useful to a smaller segment of the community, and that would not be popular.
After the talk, Ms. Taylor thanked our speaker and presented a framed, autographed copy of the lecture announcement. She announced that Mr. Smith was elected to membership of the Society.
She made the housekeeping announcements, except one. The Cosmos Club has stopped charging for parking, and there will be no more parking announcements. An era has passed. Your recording secretary is sad.
She announced the next meeting. Finally, at 9:46 pm, she adjourned the 2,264th meeting to the social hour.
The weather: Cloudy and misty
The temperature: 5°C
Ronald O. Hietala,