On the July 4 2008 weekend, I spent the time on the Mall in Washington as part of the American Folk Life Festival. Each year, this festival has three themes, and as 2008 marks the 50th anniversary of the establishment of NASA, the agency was one of the themes. I was asked to be part of that and was of course delighted - until I arrived.
I was given a table and two rocks. They were not even real rocks, but models of rocks. Great. But as I teach kids, you have to look beyond the "obvious" and try to understand what we are looking at - the whole meaning of science.
It turns out that one of these "rocks" was a model of a comet (Tempel 1) and the other was a model of an asteroid (433 Eros). The header image at the top of the window is a collage of another asteroid, Ida. The collage (all images of Ida) was taken by the Galileo Spacecraft in 1993, while on it's way to Jupiter.
Tempel 1 is a periodic comet - which means it returns near us at various times (like Halley's - every 75-76 years). However Tempel 1 visits us every 5-6 years. Comets have some rock base but they are largely made of different kinds of ice (water, ammonia, carbon dioxide, etc) and some of these could have hit the Earth in it's early formation and seeded life here. Some scientists theorize that 50% of the water on Earth originated from comets.
This is what Tempel 1 looks like:
It's about 8 miles at it's widest and 2 miles at it's narrowest.
Eros is an asteroid that in in an orbit around the sun that takes it largely between Earth and Mars. (I thought all asteroids were in orbit between Mars and Jupiter but some are not. 433 Eros is about the size, shape, and some would say personality, of Manhattan. oops.
It's thought that asteroids (made almost entirely of rock) may have caused Mass Extinction Events several times during the life of the Earth. Imagine being hit with a rock the size of Manhattan? Many scientists again theorize that one of these events caused the demise of the dinosaurs on Earth. Remember that dinosaurs lived on this planet for more than 30 times as long as we humans have been here. Our type of specie (homo-obnoxious) is about 3.5 million years old (and I'm feeling it). Dinosaurs roamed this planet for about 100 million years! It's not that the Earth was broken up by that event (thought to be in the gulf of Mexico north of the Yucatan peninsula, about 65m years ago), but that the impact of a large asteroid hitting us would have caused a "nuclear winter". That means so much dust and debris would have been thrown into the atmosphere, that there would have been a severe reduction in sunlight and a resulting decrease in plant life, aka food. That could have lasted for thousands of years.
So, with our technology, it's interesting -- to say the least -- to investigate what these things -- comets and asteroids - are made of, what their orbits are and whether we are at risk.
So, what's special about these two (Tempel 1 and Eros)? Well, these photos are not from telescopes. We've been to these two, and we've landed on both of them. It was interesting at the Festival to see the look of incredulity of people when I told them, yep, we've landed spacecraft on asteroids and comets.
The mission to Tempel 1 was called Deep Impact, which sort of describes the landing. The spacecraft was launched on January 12, 2005. It travelled 270m miles (430m km) arriving at the comet that same year on July 3 (how about that, 1 day before July 4! Coincidence - I don't think so). That meant that at that time, it was the fastest spacecraft to date, traveling at 64,000 mph (103,000kph). For reference, humans on the shuttle and space station travel at a leisurely 17,500 mph (25,000 kph).
The Deep Impact spacecraft had two parts, an orbiter and a landing probe. The lander was essentially a large brick with a camera in front (and some instruments). The orbiter slowed down to match the speed of the comet, and released the probe in front of the comet to see what would happen. A full description of the mission can be found here and at the bottom of that page there are photos and a movie taken from the impactor as the comet sped into it.
The mission landed 50 years after Bill Haley and his band (The Comets) had the first Rock and Roll hit : Rock around the Clock. The band members reunited for a concert at the Jet Propulsion Lab in Pasadena and sang the song once more for the scientists and Engineers. The band members were at that time, between 71 and 84 years old. Sweet. And in return the Space community named a comet (79896 BillHaley) in tribute.
See the link between art and science?
The mission to Eros was called NEAR. The acronym is a double-entendre. The first meaning is near-Earth Asteroid rendezvous. The second meaning is "duck". Last year, for example, an asteroid came as close to us as half the distance between the Earth and moon. In space terms, this is not very far. And. this is not uncommon. Thus, since the first realization that asteroids may play a significant role in the life of the solar system, a network of amateur and professional (civilian and military) observatories routinely watch the skies. To see the NASA page on Near Earth Orbit observations and watches, go to there website here.
In 1994 we watched as Comet Showmaker-Levy collided with Jupiter -- with images taken from the Keck Observatory:
Remember that Jupiter's volume is equal to about 1300 Earths, and those yellow flashes are impacts. Each of the two smaller impact areas is the size of Earth.
Anyway, again, I digress. NEAR launched in 1996. It first flew by Asteroid Mathilde on June 27 1997 (flying 1200km above it's surface and recording images and taking compositional readings.
Here's an image of Mathilde (btw, it's about 35 miles wide (50km)):
When it arrived at Eros in late 1998, the spacecraft was found to have software problems that delayed it's ability to settle into orbit. Engineers and programmers gradually worked through the problems and by December 2000, the spacecraft was orbiting 20 miles (35 km) above the asteroid, at a relative speed of about 200 mph. The closest orbit put the spacecraft 3 miles above the object (remember Mt Everest is almost 5 miles high).
This is an image taken from the spacecraft. The are you are looking at is an area about 50 yards across but at the time it was taken, was about 30 million miles away from us!
You are looking at the surface of an asteroid. I'd just like you to ponder that for a while.
Starting on January 24, 2001, the spacecraft, coming to the end it's fuel, was programmed to land on the asteroid (it's still there).
To the surprise of the controllers, the spacecraft was undamaged and operational after the landing at an estimated speed of 1.5 to 1.8 meters per second (thus becoming the first spacecraft to soft-land on an asteroid). After receiving an extension of antenna time on the Deep Space Network (a subject in itself, but is essentially an Earth-based network of telescopes), the spacecraft's gamma-ray spectrometer was reprogrammed to collect data on Eros' composition from a vantage point about four inches from the surface where it was ten times more sensitive than when it was used in orbit.
(Gamma-Rays are important and I will talk about them in the deep space section of this site. They tell us things from the early days of the universe to the workings of "black holes").
The last signal was received from NEAR about a month after the landing. Why did the spacecraft not last longer on the surface. I believe that the engineers expected the spacecraft to crash and not land, so they did not build in any long term communications nor science capabilities. They were as surprised as anyone that the spacecraft managed a soft landing.
These successes with robotic missions whetted the appetite for NASA to do more. We learn from each success and from each failure, and we are getting better at our programming, engineering and launch of these amazing instruments.
So, what happened to the Deep Impact spacecraft after it dropped the probe on Tempel 1? Weeell. It turns out that this spacecraft still had a lot of fuel, and scientists and engineers realized that they could re-use the spacecraft to visit other objects. So, the spacecraft - while remaining in orbit outside the orbit of Mars- was reprogrammed to visit another comet - Hartley. It will arrive there in 2010. On it's journey to Comet Hartley, the spacecraft is spending it's time looking for planets that orbit around other stars - other solar systems. Right now, we call these exo-solar planets.
As this is the work of two missions "glued" together" (the hunt for exo-solar planets, and visiting a second comet), the program has been renamed EPOXI.
The successes of Deep Impact and NEAR led to more ambitious planning.
If we could reach these objects, asteroids and comets, could we go there, collect samples, and bring them back to Earth for study. (Just as Astronauts did with moon rocks!).
In August 2001, the Genesis spacecraft was launched. It travelled close to the sun, collecting solar wind particles and returned them to Earth. The main parachute did not open when the spacecraft returned in 2004 and the spacecraft slammed into the Utah desert. While the spacecraft itself was naturally badly damaged, the collectors were not. Using technologies developed to save the material, by the following year, it was realized that the collectors were intact and the material started to be sent to research institutions for study. It is estimated that 85% of the solar wind material was saved and is now being studied in research institutions around the world.
For those of you with a bit of a dark sense of humor, here is the spacecraft coming home:
As a result of the Genesis mission, we are dramatically increasing our knowledge of the makeup of our Sun. How it works, and the nature of the material ejected by our star.
As spectacular, we had launched before Genesis, a mission to visit another comet (Wild 2 - pronounced two, I mean "Vild"). This mission would travel 3 BILLLION miles, cross within 4 miles of the comet - within its "coma", capture comet material in a new material invented for the purpose, and return the comet material to Earth. The program was called Stardust.
Stardust was launched in 1999. Obviously, the landing "issue" with Genesis was of concern, but again, engineers were able to dissect the problem and reprogram the Stardust spacecraft during its voyage.
The spacecraft opened it's collector bays before the flyby of the comet on January 2, 2004. Using a material called Aerogel, one side collected dust and particles from the comet, the other side collected particles from interstellar dust.
Following the encounter, the collector bays were closed, and the spacecraft headed homeward. Just before reaching Earth's orbit, the spacecraft released a lander containing the samples. It landed perfectly in the Utah desert at about 3am on January 16, 2006.
Scientists are being extremely cautious in extracting the comet and solar particles from the Aerogel collectors. For two reasons. We don't want to contaminate the material, and vice-versa.
About Aerogel: Remember Velcro? That was invented by NASA to make it easy for astronauts to attach and detach things to manned spacecraft. At first, Velcro was an extremely expensive material and now it's a household good.
Aerogel is a similar phenomena. Aerogel is 1,000 times less dense than glass, another silicon-based solid, and looks like styrofoam, but MUCH lighter.
When the spacecraft flew past the comet, the impact velocity of the particles in the coma as they were captured was 6100 metres per second, up to nine times the speed of a bullet fired from a rifle. Although the captured particles were each smaller than a grain of sand, high-speed capture could have altered their shape and chemical composition — or vaporized them entirely. To collect the comet particles without damaging them, scientists and engineers needed to develop a substance that would be porous and sponge-like and in which, 99.9 percent of the volume is empty space. When particles hit the aerogel, they buried themselves in the material, creating a carrot-shaped track up to 200 times its own length, as it slowed down and came to a stop — like the track an aircraft makes in setting down on a runway and braking to reduce its speed gradually. Since aerogel is mostly transparent — a property earning it the nickname "solid smoke" or "blue smoke" — scientists use these tracks to find the tiny particles. The process of removing the particles, as I mentioned above, is painstaking, and the science on the cometary material is only now beginning to get underway.
Aerogel is thus incredibly light and if developed commercially (it is), it would become an amazing insulator for houses, clothes, cars, etc.
More than 1,000 square centimeters of aerogel collection area was provided for each type of particle cometary and interstellor). The collector tray contained ninety blocks of aerogel in a metal grid. The grid looks like an ice cube tray; the round collector is about the size of a tennis racket.
Here's what the collector looks like:
The bluish stuff is the Aerogel.
Stardust capsule with aerogel collector deployed
As I mentioned, the aerogel was packed in a Sample Return Capsule (SRC) which was released from the spacecraft just before reentry, for a separate landing on a parachute. This time, the parachute worked just fine. The rest of the spacecraft fired its engines, taking it back away from the Earth.
The following picture shows the journey travelled by Stardust:
So what happened to the Stardust spacecraft?
Well, remember Tempel 1, the comet that Deep Impact visited? Stardust is going back there to see what the comet looks like years after the Deep Impact probe hit it. It will arrive at the comet in 2011.
And, so have we learned that comets seeded life here? Not yet. Wild 2 has not yet shown it contains amino acids, some of the building blocks of life, but this comet still has a lot to teach us, and there are a lot of asteroids and comets. How many are there?
Well, below is a picture showing all named asteroids:
And here is a picture of all named comets:
Note their direction.
So, to sum up. From sitting at a desk with two simulated rocks, I've gone on a multi-billion mile ride to asteroids and comets. We've learning how to do things better, like reprogramming in-flight to improve and even salvage missions, and how to reuse spacecraft.
We have not yet discovered the basic building blocks of life, but we're finding more and more components.
We are also increasingly cognizant of the threats posed by asteroids and comets to life on our planet, and we are mobilizing to look for problems - so far none exist in my lifetime.
One last thing. All the work of NASA, it's science and human missions is performed with less than 0.1% of the US Defense budget. What if it was 0.2%?