Tuesday, May 31, 2005

The future of the Hubble Telescope -- Part III

So now that we've seen some reasons that people espouse for not servicing the Hubble Space Telescope, I'll present my arguments why we should service Hubble. (Let me state for the record that these are personal opinions, not necessarily those of my employer or anybody else, etc., etc., etc.) Some of these were hinted at before, but I'll spell it out explicitly here. :)
  1. The Hubble Telescope can be completely repaired. With new batteries, new gyroscopes, and two new cameras, the Hubble Space Telescope could last up to ten more years. Without repair, it will not last more than two.
  2. The Hubble Telescope has unique capabilities that will not be replaced any time soon. Hubble's power to see blue light sharper than from the ground and its power to see ultraviolet light invisible from the ground have no planned replacement. It would hurt astronomy to lose these abilities.
  3. Hubble has two brand new cameras ready to be installed. Two new cameras, one replacing a broken camera on Hubble, and the other replacing an aging instrument that's still working, have already been built. It would waste millions of dollars not to use these instruments. There has been talk that these two cameras could be put on a "Hubble Lite" telescope, but as of now no such design exists, and more importantly no money exists to build such a telescope.
  4. It will be at least 7 years before the next space telescope is ready to fly. Not much more to say there, other than, knowing NASA, it could easily be 15 years or more before the actual launch.
  5. Hubble has captured the hearts of people around the world. NASA and astronomers have done an outstanding job showing off Hubble's accomplishments. Many people forget that the Hubble Telescope started off with blurry vision that was fixed by astronauts a couple of years later. Since that time, we have gotten amazing pictures of the distant universe, detailed looks at nearby galaxies, and fantastic shots of amazing things in our own galaxy.

So, there you go. Make up your own mind about what you think should happen to Hubble, and let your representatives and senators in Congress know. They control the purse strings in all of this!

Monday, May 30, 2005

The future of the Hubble Telescope -- Part II

So, as promised, here are some arguments people have used against servicing the Hubble Space Telescop which I consider somewhat suspect. Some of these arguments have been put forward by people who should know better, such as high-level NASA people.
  1. Hubble is dying. This is a partial truth. If left alone, the Hubble telescope will die. But the Hubble was designed to be repaired -- many of its parts, such as the failing gyroscopes that are threatening Hubble now, have been replaced many times already. Although Hubble is sick right now, a successful repair mission will make it as good as new, and ready to serve out another 5-10 years before retiring.
  2. Hubble's replacement is being built right now, so there is no need to repair Hubble. This refers to the "James Webb Space Telescope" (JWST), which is a larger telescope than Hubble with a planned launch no earlier than 2012. The JWST will be a great telescope, but it does not replace Hubble. To save money, the JWST is being built for a narrower purpose than Hubble -- to look at red light and near-infrared light (heat). This makes the JWST perfect for researching the furthest galaxies in the Universe, because the expansion of the Universe shifts their light into the red and near infrared. But Hubble is also very capable of taking data in the blue and ultraviolet light, which is important for studying nearby stars and galaxies. When Hubble dies, no space telescope in orbit, being built, or even planned, will be able to study. Even more, ultraviolet light is blocked by the atmosphere, so telescopes on Earth won't be able to study this light either. Hubble has unique capabilities that its "replacement" won't have.
  3. Ground-based telescopes can now see just as sharp as Hubble. This is true in the infrared light, because ground-based telescopes now have "adaptive optics," which allow them to correct the blurring caused by Earth's atmosphere. But these systems don't yet work in visible light, so Hubble still beats Earth-based telescopes for clarity of vision!
  4. Robots can do the job cheaper and without risk to humans. I wish this were true! But to date, no robot has been tested successfully in space. In fact, a NASA experiment to show that a robotic spacecraft can successfully meet up with another satellite, DART, experienced several problems that have yet to be understood. The chances that a robot could be ready in the two years or so Hubble has left to be serviced before it would die from being left alone are very small, and the costs are not well constrained at this point.
So next time I'll explain why I think it is worthwhile to try and service the Hubble with a space shuttle mission.

Friday, May 27, 2005

The future of the Hubble Telescope -- Part 1

Over the past several months there has been quite a bit of talk about the future of the Hubble Space Telescope. The previous NASA administrator, Sean O'Keefe, announced a while ago that there would be no more missions to service Hubble. Then, after an outcry from scientists and the public, he decided to consider alternatives, such as a robotic servicing mission. Recently, the new NASA administrator, Michael Griffin, announced that he was more seriously considering a manned servicing mission to fix Hubble.

Several of the arguments used agains fixing Hubble are not very good arguments, but some are very good. Let's start with the good arguments against fixing Hubble:

  1. A repair mission is expensive -- The total cost of a mission would be over a billion dollars. That money would have to come from other NASA programs, such as future space telescopes.
  2. If the shuttle were to lose part of its protective shielding, there would not be enough time for a rescue mission -- This is true unless a second shuttle happened to be put on the launch pad, ready to go on a rescue mission at a few days' notice. This would raise the cost of the mission a lot.
  3. Hubble has outlived its planned lifetime -- Also true; it was hoped that Hubble would last 5 years, maybe 10. And its up to 15 years!

Next time I'll talk a bit about some of the flimsier arguments used against a servicing mission, and then in the last of three parts, I'll give what I feel are good arguments for servicing Hubble.

Wednesday, May 25, 2005

Nearing the edge of the Solar System

Voyager 1, that intrepid spacecraft launched in 1977, has entered the last reaches of the solar system (depending on how you define the solar system). What does this mean?

The sun blows a wind of charged particles at speeds of up to 500 miles per second. This solar wind is created by the sun's magnetic field and is responsible for the Earth's auroras. Even out beyond the orbit of Pluto, the solar wind essentially controls all of the magnetic and electric dynamics of the solar system.

As the wind moves outward, it thins out because it needs to fill more space. Eventually the solar wind runs into the winds of other stars and of our galaxy itself. The solar wind abruptly slows way down in a termination shock, which also heats up the wind. The wind piles up, becoming denser (though it is still a far better vacuum than humans can make on Earth!).

Voyager 1 has now definitely crossed this termination shock and entered the heliosheath, a region where the solar wind continues to dominate, but moves more slowly. Eventually, the Voyager probe will cross the "heliopause," where the solar wind will end and the interstellar gases of the Milky Way galaxy will rule.

So, how far away are all these things? Right now, Voyager 1 is about 9 billion miles from the sun, or 94 times the distance from the Earth to the Sun. For reference, Pluto is, on average, 40 times further away from the sun than the Earth. The distance to the heliopause is uncertain, but is thought to be around 110 times the Earth-Sun distance. Voyager 1 should have enough electricity and fuel to communicate with the Earth until the year 2020, at which point it should be almost 150 times the Earth-Sun distance away, or almost 14 billion miles!

But does the heliopause really mark the edge of the Solar System? The heliopause marks the limits of the sun's magnetic influence, but the sun's gravitational pull extends further yet. The Oort Cloud, comets in giant orbits around the sun, may extend out nearly one light year, or six trillion miles. That's over 550 times the distance to the heliopause! Voyager 1, at its current rate of speed, will take almost 18,000 years to reach this distance and become a true interstellar spaceship.

Tuesday, May 24, 2005

New planet discovery!

Planets are being discovered around other stars fairly commonly these days, so it is rare that a single new planet is quite interesting.

So what is interesting about the new planet, a Jupiter-sized planet around the unpronounceable star OGLE-2005-BLG-071? It is the method by which the planet was detected.

Most planets have been discovered by measuring the movement of their parent star. A planet's gravity causes the parent star to move slightly -- in the case of Jupiter's orbit around the sun, the sun moves a distance about equal to its own diameter every 11 years. It's amazing that this motion can be detected, but this is the most efficient way of discovering planets, with over 140 announced planets!

Another method of discovering planets is to look for the change in light from a star when a planet passes in front of the star, blocking out some of the star's light. This method is hard, because the total change in the light from a star is only about 1%. Even worse, it takes special geometry for these transits to happen, so only a small fraction of stars with planets will show transits. Even so, a handful of planets have been discovered this way.

Of course, you can always try and take direct pictures of a planet, but this is hard, because planets are over ten thousand times fainter than the stars they orbit! Imagine trying to take a picture of a flashlight located a few inches away from a spotlight -- it's hard! A few potential planets have been found this way, but they have yet to be confirmed.

The planet in OGLE-2005-BLG-071 was discovered by a totally different method, gravitational micro-lensing. Several hundred times a year, a star in our galaxy wanders directly in front of a much more distant star as seen from the Earth. The gravity from the star in front acts like a lens and magnifies the background star, making the background star appear brighter. These "microlensing events" have been observed for years and are well-understood.

Earlier this year, one of the searches for these microlenses, the OGLE survey, detected a star getting brighter in the manner that suggested a microlensing event was occurring. The star was monitored closely. But instead of a "normal" event, where the background star steadily gets brighter, reaches a peak, and then fades, this star showed two separate peaks in brightness separated by three days. When the astronomers calculated what type of star system was needed to explain this light curve, they figured out that there was a parent star and a companion planet with a mass 0.7% that of the star. As a comparison, Jupiter is 0.01% the mass of the sun. However, since we do not see the parent star, only its gravitational effects on the background star, the parent star is probably low mass, perhaps as low as one-tenth the mass of the sun, meaning that this planet could be as small as Jupiter, and at most several times the mass of Jupiter. This compares very well with the masses of planets discovered by other methods.

So, this planet confirms that it is possible to discover planets by yet another method, gravitational lensing. The discoverers are continuing to analyze their data to try and learn more about the planet, like its exact mass, its distance from the parent star, and the distance from us to the planet.

Monday, May 23, 2005

An Astronomer's Monday

So many people have the idea that astronomers work every night at the telescope and that we sleep during the day. This is, alas, a romanticized view of astronomy. If we are lucky, we'll get a week or so at the telescope every six months. So, what do astronomers do on a typical day?

It's been a few weeks since I was last at the telescopes, so I'm on a pretty "normal" schedule right now. I got in about 8:30 this morning, and started by reading emails that had piled up over the weekend. Most of them weren't very interesting -- typical bureaucratic emails reminding us that parking pass applications are due, that we should be certain to lock up our bikes to prevent them from getting stolen, and that the fans in the Chemistry building will be down for repair on such-and-such a date. Exciting, no?

This was followed by a quick browsing of research papers that were published over the weekend. A few interesting papers were there, but probably nothing you would find very exciting, unless you are interested in "gray dust."

I'll now spend the rest of the day analyzing data from recent telescope runs. I have some computer tests I'll be running to see how effective my analysis is. Again, nothing exciting to report yet!

This is a rather typical day for most astronomers. If it were during the school year, we'd also have various academic meetings to go to and classes to teach. So, this is not a glamourous, rock-star life (darn!). Nor are we hermits living on top of a mountain and isolated from the doldrums of everyday life. But every once in a while, we get that little spark that produces an interesting result. And when I do, I'll be sure to share it. :)

Friday, May 20, 2005

Saturn and the Death Star

Wednesday night a group of astronomers joined other crazed nerds enthusiastic fans to see the midnight showing of Star Wars: Revenge of the Sith. In one scene at the end of the movie, you see Darth Vader and the Emperor watching the beginning of construction of the Death Star.

Whenever I see the Death Star, I am reminded of this photo of Mimas, a moon of Saturn. It looks a lot like the Death Star, but the original Star Wars (A New Hope) was released nearly three years before this photo was taken! The resemblance is uncanny and almost scary!

The large crater on Mimas is named "Herschel," after the astronomer Williams Herschel, who discovered the moon in 1789. The impact that created this crater nearly ripped the moon apart. The terrain on Mimas shows ripples and other evidence of this incredible event.

Let us hope the Galactic Empire does not decide to make use of Mimas and destroy the Ringed Planet!

Tuesday, May 17, 2005

Stuck in the sand...

So the Mars rover Opportunity got a bit too wild while driving recently and got stuck in a sand dune. On Earth, we know that rocking back and forth is a good way to get un-stuck, and if all else fails, call AAA. But on Mars, and when talking about a multi-million-dollar robotic laboratory, rocking is not an option, and AAA will take too long to get there. So the Mars rover team had to do some tests to find a way out of the sand dune.

Due to some smart thinking, the team has a duplicate rover here on Earth. So they spent a couple weeks meticulously reproducing a Martian sand dune. Since we don't have any Martian sand, the scientists had to use close-up pictures of the sand taken by the rover and then mix up a similar-looking concoction here on Earth. They ended up using a mixture of sand, clay, and diatomaceous earth (dirt made of tiny shells from microscopic plants). After testing with the Earth-based rover, the scientists then were able to send instructions to Opportunity to begin moving out, a few inches at a time.

As of right now, this method seems to be working! In a few more days, Opportunity should be prowling the Red Planet once more. I bet you that the Earth-based drivers are a bit more careful to avoid dunes in the future, though!

You can read more of the ongoing adventures of the Mars rovers Spirit and Opportunity at NASA's Mars Exploration Rover Homepage, which also includes lots of cool pictures the rovers have been taking. Be sure to have 3D glasses (the kind with red and blue lenses) so you can see what Mars looks like in three dimensions!

Saturday, May 14, 2005

Back on the air...

I disappeared for far too long, always planning to finish updating the rest of the web site and then getting back to blogging. Well, while sitting in the snow and rain at the CTIO Observatory in Chile, I finally got around to doing just that. So, feel free to explore the site, and I'll be more regular in blogging.

Here's wishing you clear skies!