All posts for the month March, 2011

Exploring a Hot/Cold Little World

This WAC image showing a never-before-imaged area of Mercury’s surface was taken from an altitude of ~450 km (280 miles) above the planet during the spacecraft’s first orbit with the camera in operation. The area is covered in secondary craters made by an impact outside of the field of view. Some of the secondary craters are oriented in chain-like formations. Courtesy NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.

Yesterday was a banner day for the folks who run the MESSENGER mission to Mercury.  The first images that the spacecraft has taken since it achieved orbit around the planet began streaming back to Earth.  Now, there have been a good many flyby images of Mercury, not all of them high-res, since we began exploring the solar system in the mid-1960s with spacecraft. But, these are the first taken from a spacecraft orbiting the planet.  This means that we’re going to (finally) get to see every bit of this world’s ancient, cracked and cratered surface.

The first images (which you can browse at the MESSENGER Web Site) are pretty detailed.  For example, this Wide Angle Camera view shows an area near the north pole of the planet.  It was taken as the spacecraft made its closest approach to the sunlit side of the surface.  The long shadows are caused because the Sun is at an oblique angle to the spacecraft, which was just about to cross over into darkness.

The polar region of the planet is of great interest to astronomers because some radar studies of the area taken from Earth seem to imply that there might be ice on the walls of those craters. Sunlight never penetrates into the craters, so that would be an exciting cache to study someday.  The water could be from impacts of comets, and studying THAT ice would tell us about the compositions of the comets that left their water behind.

The full imaging mission, which is planned to last for at least a year, begins on April 4; currently scientists and engineers are testing the spacecrafts systems and instruments to see how it is responding to its permanent home in orbit around Mercury — and enduring the harsh environment so close to the Sun.

Mercury might seem the last place you’d want to visit — and it probably won’t be the subject of human exploration for a long time. It’s a pretty extreme place, experiencing the widest surface temperature swings of any place in the solar system. It has little to no atmosphere, and its surface takes a radiation pounding from the Sun. Still, if you’re going to completely understand the solar system you inhabit, it pays to study the extreme places as well as the temperate (relatively) ones. In Mercury’s case, astronomers have a very specific set of questions to ask to help understand this place:

Why is Mercury so dense?  What is its geologic history? What is the nature of its magnetic field? What is the structure of the planet’s core? What are the unusual materials seen at the poles?  What volatiles (gases) are important at Mercury?

Some of these questions are those you’d ask at any planet to help you understand its composition and history.  So, with Mercury, we’ll finally get some closure on the last of the major planets of the solar system.  The only remaining world to visit (and there’s a spacecraft on the way) is dwarf planet Pluto. New Horizons will give it a swing-by in 2015, on its way out to explore the outer solar system. Another extreme, to be sure, but now we’ve got precedent with Mercury.

The Deaths of Stars

This HST mosaic image of the Crab Nebula shows a six-light-year-wide expanding remnant of a supernova explosion. Courtesy STScI.

Stardeath produces some of the most intricate-looking objects in astronomy. If you have ever gone to the Hubble Space Telescope’s Web site and searched for planetary nebulae, you know what I mean. Giant stars produce giant explosions, like the long-known Crab Nebula.

The Eskimo Nebula (NGC 2392). The intricate "face" is a bubble of material being blown into space by the central star's intense "wind". Courtesy STScI.

This Hubble Space Telescope image shows us what the supernova remnant is made of (hydrogen gas, particles of heavier elements), and also shows us the structure of the nebula and how it’s influenced by the neutron star at the center. That neutron star is what’s left of the original star — a dense object spinning more than 30 times per second.

Stars like the Sun go a bit less violently, huffing off their atmospheres for millions of years before collapsing to make white dwarfs. The radiation from the central star continues to light up the remains of the former star, creating complicated visions of stellar death. The Eskimo Nebula (right), is a fine example of such a sun-like star’s death. The remains are called a planetary nebula, one of those odd misnomers in astronomy that has nothing to do with a planet, but is a nebula. This sunlike star began to die some 10,000 years ago, blowing bubbles of gas out away from itself and flinging its outer atmosphere to space. Our own Sun might look like this some billions of years from now.

Well, I’ve been long fascinated with the images of star death, ever since I wrote my first book (with Jack Brandt), about Hubble Space Telescope science (called Hubble Vision).  A few years ago when I did an update of one of my more-popular planetarium shows, called Hubble Vision 2, I had a great selection of star death images to choose from to tell the story of stellar demise. I wrote about sun-like stars, “Hubble’s images of these stars in their death throes comprise a haunting gallery of destruction.”

As is always the case with my shows, I knew that the soundtrack artist (who also happens to be my husband and co-producer) would find a way to make the scene  memorable with his trademark space music and video choreography. The scene in the show is a solemn, beautiful procession of planetary nebula images that bring home to audiences the majesty of a star’s passing.

Fast-forward a few years to this month, and Mark has now released the music from that show soundtrack in an album called Geodesium Stella Novus (where you can preview and buy the album if you’re interested). And, he created a music video based on that planetary nebula scene that really does bring home the majesty of that haunting gallery of destruction we first introduced in the show. We created a fulldome version of the music video, which you might get to see someday at your local digital planetarium.

But, we’ve also got a “flat-screen” version available on our Youtube channel for people to watch and I’ve embedded it below.  The piece of music is called “Light Echoes”, and it accompanies these gorgeous views of star death, ranging from supernova remnants to planetary nebula, as cosmic art.  It’s not a new concept — the universe as art. But, you have to admit, when you see the way nature has arranged the aftermath of stardeath, it can look evocative, haunting… and artistic!