01/19/2005
Two Jobs Well Done
Christiaan Huygens was quite a guy. He discovered polarized light (you may have a pair of Polaroid sunglasses), developed the wave theory of light (from which the laws of optics were derived) and invented the micrometer (an instrument used to measure small dimensions such as the thickness of a wire, a hair or a sheet of metal). He was also the first to use a pendulum to regulate a clock and worked on improved lenses for the newly invented telescope. It was 350 years ago, in 1655, that he pointed one of his telescopes at Saturn, wanting to study its rings. Huygens was surprised to see not only the rings but also a large moon orbiting Saturn. Today, his namesake rests on the surface of that moon.
In last week’s column, we talked about the outstanding accomplishments of the Mars rovers Spirit and Opportunity and their mentors, the dedicated workers at Jet Propulsion Laboratory (JPL). Last Friday (January 14), the JPL crew and especially their counterparts in the European Space Agency (ESA) and the Italian Space Agency could celebrate another spectacular success. The Europeans have waited for over seven years to learn the fate of their Huygens space probe. It was in October of 1997 that NASA launched the Cassini-Huygens mission. The Cassini spacecraft (designed and built by JPL) had been cruising around Saturn and its moons for some time when, on the day before Christmas, it turned loose ESA’s Huygens, a 705 pound space probe named appropriately after Titan’s discoverer. Last Friday, Huygens, which is shaped like a wok, deployed its parachute and floated down through the thick, murky atmosphere of Titan.
Last week, we discussed JPL’s early problems with the Spirit rover on Mars not waking up on schedule and how it was finally brought into line. With Huygens, there was no second chance. It had to wake up upon entering Titan’s atmosphere, snap pictures and take data on its way to impact on Titan’s surface. It was hoped that Huygens would continue to snap pictures and collect data for at least a few more minutes after impact. Huygens performed beautifully, sending back data for about 2 hours while descending through Titan’s atmosphere, which is mostly nitrogen. Clouds of methane were detected at an altitude of about 12 miles and a fog consisting of methane or ethane was observed near the surface.
Huygens hit the ground at a speed of about ten miles an hour and the ground was found to have the consistency of wet sand or clay with a thin crust. The ground was identified as a mix of dirty water ice with hydrocarbon “ice” of various organic compounds. Huygens gathered its data and transmitted it back to Cassini for transmission back to Earth. A January 18 report from ESA indicates that Cassini got an hour and 12 minutes of excellent data from Huygens on the ground before Cassini disappeared over the horizon out of contact with Huygens. Radio telescopes on Earth continued to track the Huygens signal, however, and the plucky probe was still transmitting away for at least three hours after landing.
It seems fitting that, 350 years after the discovery of Titan, Huygens sent back some 350 pictures. It was hoped that 700 pictures might be returned but one data channel succumbed before this could be accomplished. Otherwise, Huygens performed so valiantly that there were tears in the eyes of some of the European workers.
Titan is unique among the many moons of our solar system in that it has a significant atmosphere, which is even denser than ours on Earth. The atmosphere of nitrogen mixed with methane and other hydrocarbons and organic compounds, is thought to have a composition much like that of early Earth billions of years ago. However, Titan is a frigid place, with surface temperatures around minus 290 degrees Fahrenheit, way too cold for liquid water to exist. (By way of comparison, Embarrass, Minnesota reported a near record temperature for Minnesota this week of minus 54 degrees Fahrenheit, the record being a minus 60 degrees, a veritable heat wave compared to the temperature on Titan.)
Titan is not a small moon and is actually bigger than the planets Mercury or Pluto. Pluto, you may recall, is having some difficulty maintaining its status as a planet after the recent discoveries of other large bodies such as Sedna out there in the far reaches of our solar system. However, after just a day of data from Huygens, some were talking of Titan as a “planet” or a whole new “world”.
What does Titan look like? You must have seen pictures on the front pages of your newspapers of what look like rocks that are possibly chunks of water ice less than a foot in size. On ESA’s or NASA’s Web sites (esa.int and saturn.jpl.nasa.gov), you can see the rock picture in color. The sky is orange while the surface and the rocks look to me as being a light pinkish color. Titan has canyons, shorelines, what look like drainage ditches, possible seas and islands. It’s almost like here on Earth except that any “seas” are composed of liquid methane or other organic compounds. Hopefully, more pictures will be shown at an ESA press conference scheduled for January 21.
Huygens sent back not only photos but also the sounds of Titan. On the ESA web site you can actually listen to the sounds recorded as the probe fell through Titan’s atmosphere. It’s a kind of swooshing sound as if Titan is saying shhhh. I heard that after Huygens landed it extended a microphone and actually picked up the sound of a brisk wind blowing on the surface of Titan. Hopefully, that recording will also be available on the Web site. How neat is that, to be able to hear the wind blow on a place over 700 million miles away?! Bravo, Huygens!
While reading about Huygens in our newspaper, the Star Ledger, I found a story about another spectacular astronomical discovery involving a spacecraft named after a famed scientist. Some years ago, I wrote about a Nobel Prize winner named Chandrasekhar and his calculations showing that a massive star would collapse to form a black hole. Later (column of 7/27/1999), I mentioned that an X-ray satellite, called Chandra in his honor, had been launched and that one of its missions was to study X-rays emitted by material being sucked into black holes.
What Chandra found is an unusual formation of two monstrous cavities surrounded by hot gas in a distant cluster of galaxies. The cavities are each about 650,000 light years across. A light year is about 6 trillion miles so you get the picture that these are indeed huge! The cavities, though humongous, may not impress you but perhaps the cause of them will. It’s the biggest explosion ever recorded, except for the Big Bang itself. And what caused the explosion? It’s the gobbling up of material by an equally humongous and ravenous black hole, precisely what Chandra was sent up to study. Another job well done.
Ohio University’s Brian McNamara, lead author on an article in the January 6 issue of Nature, says he “nearly fell out of his chair” when he saw the Chandra data. The explosion involved the black hole gobbling up the equivalent of 300 million suns! McNamara is quoted on Ohio University’s Web site as saying that this 300 million suns is almost as massive as the black hole that swallowed it. I conclude therefore that the black hole now contains at least 600 million suns’ worth of stuff. This means that if the center of the black hole were our Sun, the hole would encompass our entire solar system. That’s one huge black hole! Thankfully for us, the explosion occurred about 2.6 billion light years away from Earth or we would all be toast!
What about those cavities? Jets of stuff from the vicinity of the black hole erupted to push back gas around the black hole to form the cavities. According to the Chandra Web site at Harvard University (chandra.Harvard.edu), the mass of gas pushed back is more than that of all the stars in our Milky Way! The explosion is so powerful that the energy from the explosion extends over a volume in space 600 times that of our whole Milky Way galaxy.
We have our earthquakes, hurricanes and tsunamis, with their disastrous consequences but, thankfully, our local black hole at the center of our galaxy is much better behaved than its distant gluttonous cousin. Otherwise, we might not be here to talk about it.
Allen F. Bortrum
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