Sunday, January 27, 2013
Sometimes pictures from other planets are so intriguing, you almost have to stop your eyes from making snap judgments. What do you see on the above image from the north pole region of Mars?
It almost looks like some sort of weird plant growth, doesn't it? But it's NOT!!! Nothing like plants could grow in the thin atmosphere of Mars, with relentless and deadly ultraviolet light from the Sun beating down on the dry surface.
What we are seeing here are streaks of darker sand rolling down the incline of pinkish sand dunes. This was taken during the spring, when warming temperatures on Mars evaporate the dry-ice coating (white color) and free the darker sand to fall down hill. Look carefully -- none of those tall dark "plants" show a shadow! To give you a sense of scale, this picture is about 1 kilometer (a little more than half a mile) across.
But what a wonderfully eerie picture those streaks of dark sand make across the martian landscape. You can already hear the "conspiracy theorists" saying that NASA is hiding the news of dark trees growing on Mars! The image, by the way, is from the wonderful HiRISE camera aboard the Mars Reconnaissance Orbiter spacecraft.
Something similar can be seen, if you check out the following summertime image from Mars' south pole region:
Here all the dry-ice (carbon dioxide) frost has evaporated -- that's what happens in summer. Where the frozen dry-ice is trapped underground, and then makes its way to the surface, it can leave grooves in the ground -- all aimed toward the central point where the gas finally built up enough pressure to escape. Seen from above, these features look like spiders. They are actually channels etched into the surface about 3 to 7 feet deep.
This spidery scene is about 3/4 of a mile across. HiRISE took this one too. Will someone in Hollywood soon be making a movie about giant spiders on Mars?
Sunday, January 20, 2013
As the Sun sets on Monday evening, Jan. 21, and you face South and look up, you should see a pretty sight. The planet Jupiter will be very close to the Moon, almost cheek to cheek with it. Their "closest approach" in the sky will be around 7 pm Pacific time.
The two just happen to look close on the sky -- in reality, Jupiter is 1,700 times further away. Jupiter is the largest planet in our solar system -- eleven Earths could fit side by side into its diameter.
As an extra treat, you get to see the bright star Aldebaran just below the Moon-Jupiter pair. Aldebaran, the reddish eye of the bull figure that gives its name to the constellation of Taurus, is a cool giant star, about 44 times as wide as the Sun. It is about 67 light years away, meaning the light we see tonight took 67 years to get to Earth. If you could see Aldebaran up close, it would shine over 400 times as bright as the Sun. But with all that distance between it and us, it's just a reddish point in our sky.
As you can see in the diagram, the Moon and Jupiter are already close tonight and will still be close on Tuesday night. But Monday is the best time to look up. Take the kids outside in the evening or make a date to be outside with someone with whom you like to spend time in the dark.
(Thanks to Sky & Telescope magazine for the diagram I am showing.)
Wednesday, January 16, 2013
The Hubble Space Telescope folks have just released a beautiful photo of a region where new stars are forming. Called by its catalog number, N11, this region of young stars and reddish glowing gas is in the Large Magellanic Cloud, one of the satellite galaxies that goes around our Milky Way. When you look at the image, bear in mind that the light we are seeing today from this galaxy left it 168,000 years ago. (In other words, the photo shows something 168,000 light years away.)
In the upper left corner, you can see the Rose Nebula, a tight round region in whose hidden center, new stars are being born right now. To give you a sense of scale, that little round gas cloud -- at the very top right -- is about 8 light years across.
In the middle of the image is the more extensive cloud of gas and young stars nicknamed the Bean Nebula (because of its shape.) Several generations of stars have been born in that cloudy region, and their adolescent energy has helped push the gas that gave birth to them into a larger and larger region.
Toward the bottom of the picture, you can see a jewel box of young bluish stars. Many are so hot they actually glow not just with blue and violet light, but with ultraviolet (what tanners call "black light.") Their energy has pushed for a while on any remaining gas from the cloud that gave them birth, so the neighborhood around them shows almost nothing of the reddish glow that signals warmer gas.
N11 is one of the largest nurseries for making stars we have ever observed. It's wonderful to have such a clear colorful image of the whole area, thanks to the remarkable instruments aboard the Hubble.
(And a personal note: the catalog number N11 is from a list of such glowing nebulae first put together in the 1950's by astronomer Karl Henize. Later in life, Henize became a Shuttle astronaut, and when it was his turn to go to space, he was a member of the Board of Directors of the Astronomical Society of the Pacific, where I was the Executive Director. He found that he had enough room in his personal kit to take a banner for the Society into space with him. We didn't have a banner, but when he offered, we of course made one up, real fast. He brought it back from space and presented it to me in a wonderful ceremony at the Society's headquarters (see photo below). It still has a place of pride on the walls of the Society's building in San Francisco.)
Sunday, January 13, 2013
Astronomers using both the Hubble and the Spitzer space telescopes have gotten an indication of weather in the atmosphere of a kind of "failed star" called a brown dwarf. Stars are so far away that, in general, they look like points of light, even in our biggest telescopes -- so this is quite an achievement.
Brown dwarfs (a name coined by Jill Tarter, the scientist on whom Jodie Foster's character in the movie "Contact" was based) are large balls of hot gas that "ain't got what it takes" to be a star. They don't have the mass to continue making energy on their own, so after a brief period of glowing from how compressed they get at birth, they just fade away. (I like to compare them to all the actors that come to Hollywood with high hopes, maybe get a role as an extra in a TV show, but never make it to be real stars.)
This particular brown dwarf (which doesn't have a name, only a long catalog number) was observed not in visible light but in "infra-red" or heat rays, which allow us to see cooler glows. Both the Hubble and the Spitzer can detect and measure infra-red waves, but they "see" them from different depths in the atmosphere of the star. Daniel Apai, one of the astronomers doing the work, compared this to medical imaging, where different kinds of instruments can see different layers of your body.
As shown in the accompanying artist's interpretation (NOT a photograph!), there appear to be huge and deep clouds in the star's atmosphere, some of them as large as planet Earth! They move around in the atmosphere as the star spins every 90 minutes or so. They may somewhat resemble the largest regularly scheduled cloud we know in the solar system, the Great Red Spot of Jupiter (see the beautiful image below, from the Galileo spacecraft which orbited Jupiter.)
But the temperature in a brown dwarf is not cool like the atmosphere of Jupiter, so the clouds are likely to be made of different stuff from clouds on Earth and Jupiter. What might condense into clouds in a region which is 1100-1300 degrees Fahrenheit (600-700 degrees Celsius) in temperature? Mark Marley, another scientist on the team, suggests they are "composed of hot grains of sand, liquid drops of iron, and other exotic compounds."
Isn't it amazing that we can now do weather reports from a star?
Wednesday, January 9, 2013
This week, 2800 astronomers are gathered in Southern California for the winter meeting of the American Astronomical Society and the news from the meeting is coming so fast and furious even seasoned astronomy fans are somewhat overwhelmed. Let me just list a few of the news stories for you for now and we will explore some of them further in future posts.
The picture I have attached above shows new information about the planet orbiting the star Fomalhaut, the 17th brightest star in the night sky (and, at a distance of only 25 light years, one of the closer stars to us.) The faint distant planet, one of the first planets outside the solar system to be actually photographed, is shown here in an image from the Hubble Space Telescope.
In the image, the bright star has been covered up by a dark disk (in the middle) that the Hubble telescope can use to block light. That allows us to see the planet and the huge dusty disk surrounding the star. The planet has an orbit that takes it around its star in about 2000 Earth years. (Compare that to a 1-year orbit for Earth and a 12-year orbit for Jupiter.) So some astronomical commentators are suggesting it might be more of a giant comet or a distant ice-dwarf (like Pluto) and not really the kind of planet we first think of when we talk about planets.
In a related story, the Kepler mission team, searching for planets that "eclipse" their stars (see earlier posts of mine on this mission), is reporting 461 new planet candidates, bringing their total number of possible planets to 2,740! Four of the new candidates are less than twice the size of Earth and orbiting where conditions are Earth-like.
Nest, teams of astronomers using orbiting telescopes have filed the most detailed "weather report" yet about clouds in the atmosphere of a "brown dwarf" -- the name we give to a failed star. These objects begin life like stars do, but can't keep making energy in the way our Sun and others stars can. It's amazing that we can now probe for the existence of Earth-sized clouds in the outer layers of these remote, faint objects.
Plus there is the possible discovery of floating icebergs on Saturn's moon Titan, an asteroid belt around the bright star Vega, and much more. (The reason there is so much news all at once is that astronomers save their discoveries for announcement at this annual winter meeting, so they can share the results with their colleagues and argue about them right then and there. With almost 3000 astronomers gathered in the same convention center, there is a good clump of experts to dissect and admire each discovery.)
More details in posts to come.
Wednesday, January 2, 2013
Scientists working with the Cassini space probe orbiting Saturn have recently identified a river more than 200 miles long on the moon Titan. You can see the river valley running into a large sea (to the right) on the radar image. Like the seas on this frigid moon, the river is not filled with liquid water (much too cold for that), but probably liquid methane (swamp gas) and ethane.
Titan has a thick, smoggy atmosphere, so the spacecraft can't just look for features like this using ordinary light. Instead, one of its instruments does the same thing that airport controllers do to keep track of aircraft. It bounces radar beams off the moon's surface and then makes an image using the radar information. On such radar pictures, dark means smooth, light means rough. You can see the smooth dark surface of the river on the accompanying picture, which makes scientists think that the river basin really is full of a flowing liquid with a smooth surface.
This is the first flowing river found on another world besides Earth. Mars has dried-up river beds, but its atmosphere is much too thin to allow liquid rivers or seas today. Titan, on the other hand, has an atmosphere thicker than Earth's, so the pressure is enough to allow liquids to flow.
Earlier radar (and infrared) images of Saturn have identified a number of lakes on Titan, including one as large as Lake Ontario. There are also images that over time, show liquid areas getting smaller and larger, as if they evaporated and then were filled again -- perhaps by rainfall. (Once again, this would be a rain of cold ethane and methane, not water.) Just like the Earth is at "the triple point" of water (boasting temperatures and pressures where water can be solid, liquid and gas), so Titan appears to be at the triple point of methane and ethane and so we can have these substances as vapor, bodies of liquid, and icebergs.
I'm just about to teach my introductory astronomy class on the planets at Foothill College starting Monday and Tuesday, and between the new pictures from Mars and Saturn (to say nothing of Mercury), we'll have lots of astronomy news to keep us occupied. If you can't attend, don't worry. I'll also continue to share the news on this blog as we go along.