Sunday, July 20, 2014
On Wednesday, August 6, the European spacecraft Rosetta is going to have a close encounter of the best kind with a comet (a chunk of cosmic ice mixed with dirt.) It's called Comet 67P (the P stands for periodic comet, meaning it comes around again and again every six and a half years.) Its more informal name is Comet Churyumov–Gerasimenko, after the two astronomers who discovered it on a 1969 photograph.
In mid-July when our photo was taken, the spacecraft was still more than 7000 miles from the comet, but it was already becoming clearer in the camera. And, as you can see, 67P/C-G is weird looking. Instrument project manager project manager Carsten Güttler said,“The images faintly remind me of a rubber ducky with a body and a head."
What could cause the icy body of this comet, which is roughly two and a half miles across, to look like this. One possibility is that it is really two comets stuck together, something we have seen in other comets (such as 8P and 103P). Or maybe it was one comet that broke apart into pieces when it got too close to the gravity pull of a big planet like Jupiter, and this odd fragment is all that's left.
Another possibility is that early in its life the comet got hit by other chunks of cosmic ice or rock, carving out big pieces of it and leaving great rounded valleys behind.
We should learn more when we get closer to this ancient icy visitor, and especially when part of Rosetta attempts a landing. Stay tuned.
In the meantime, here is a great animation of the images from this past week, showing the comet spinning in the majestic darkness of
Sunday, July 13, 2014
An international team of astronomers recently reported a wonderfully strange discovery. They found the faint, cold "corpse" of a dead star, not by detecting any light from it, but through its gravity grip on another star corpse with which it shares a system. It's quite a story!
To follow it, we need to take a brief excursion into the gruesome deaths of stars. All stars collapse at the end of their lives, but stars with different amounts of mass (stuff) die differently. Less massive stars (like our Sun) eventually die by collapsing into a ball not much bigger than a planet -- such a white-hot but tiny corpse is called a "white dwarf." They start out as really hot, but cool off as they shine away their light and heat into the darkness of space.
More massive stars have a more complicated death in store for them. They die in a sudden event, where the core of the star collapses catastrophically, while the rest of the star blows up in a giant explosion called a "supernova." We have discussed such explosion in several posts.
What interests us today, however, is the tiny core of the star which is super-squozen (that's a technical term!) by the star's death. It's typically not much bigger than your average suburban town, and called a "neutron star" -- because in it all the atoms lose their identity and become neutrons.
Such a neutron star, surrounded by an "atmosphere" of materials from the messy explosion of the rest of the star, can sometimes be detected by faint pulses of radio waves it gives off, and is then called a "pulsar." (A watch company "borrowed" that name, but we astronomers had it first.)
So now here's the discovery. Astronomers using radio telescopes first discovered a pulsar in the constellation Aquarius, indicating that a neutron star was revealing itself to us. But the pulsar showed signs of wobbling, as if something with strong gravity was orbiting around it and pulling on it. Careful measurements reveal that the orbiting object is a white dwarf, and it takes only two and a half days to revolve around the neutron star. (Remember that Earth takes 365 days to go around the Sun, so these two star corpses are in an intimately close dance.)
To their amazement, when other astronomers tried to find the light or heat of the white dwarf companion, they COULDN'T -- not even with the biggest telescopes. That white dwarf must be so old that it has cooled down below the level where we can find it (at its distance of about 900 light years.) This makes it the coldest, dimmest star corpse ever found. If you are into star corpses, and we astronomers really are -- this is a big deal. It's remarkable that with today's technology, we can know this white dwarf is there not by its light, not by its heat, but just by its pull on another dead star nearby.
Note: Our image is just a painting, not any kind of photograph. It shows the pulsar on the left (with two beams of radio waves coming from it) and the white dwarf on the right. Although we can see light coming from the white dwarf in the painting, in real life the star is so faint and far away, no light from it is detectable with today's instruments.
Friday, July 4, 2014
For those of you who don't get to see fireworks today (July 4), here is an image of cosmic fireworks for your enjoyment. The glowing ring on our picture (taken with the Hubble Space Telescope) shows material ejected long ago from a star whose total explosion we saw in 1987. Recently, earlier debris from the star has been hit by the fastest moving material from the star's final explosion. The shock of collision has set knots of thicker material in the ring to glow like a necklace of sparklers.
The dramatic explosion at the end of the life of a star is called a "supernova," and this particular supernova is located in one of our closest neighbor galaxies, the Large Magellanic Cloud, about 168,000 light years away. We wish it were closer, but a visible supernova is a rare event. This was actually the first supernova explosion we have been treated to since the invention of the telescope in 1609-1610. It's been given the extremely clever name Supernova 1987A (the first such explosion seen in 1987.)
The huge star whose explosion we saw in 1987 had been losing some of its mass in earlier periods of its life and was surrounded by a cloud of its own debris. Later a wind of hot particles had blown from the star as it went through a different stage of its development. That wind had made a cavity in the gas around the star.
Now the material from the star's actual explosion, which has been moving for 27 years at great speed, has reached the inner walls of this cavity and is colliding with thicker blobs of the older material. That's the glowing ring we see so clearly in the Hubble image.
If you want to see a time lapse movie made of Hubble images taken each year as the ring started lighting up, you can see it at:
Happy fireworks day!
Tuesday, July 1, 2014
Last night, thanks to the Wonderfest organization in San Francisco, I got a chance to see a science fiction film that was in theaters for so short a time that if you blinked, you probably missed it. It's called "Europa Report" and it is the story of a crewed expedition to Jupiter's intriguing moon Europa. This world, one of the four large moons of Jupiter discovered by Galileo, is an ice-covered ball that may well have a large liquid ocean under its surface.
You can see Europa's cracked surface on the picture I have posted above. (This is actually a montage of images from NASA's Galileo spacecraft, with additional image processing by Professor Ted Stryk to bring out more detail.) One possibility is that the dark cracks we see are places where material from deeper inside the Moon (perhaps even from the liquid ocean) is seeping up toward the surface.
In the movie (see the poster below), future astronauts (from a private space company) go to Europa to search for evidence of life. The complex story is told by interweaving the view from cameras in their suits and in their cabins, with footage they recorded for sending back to Earth and interviews with the mission controllers, who eventually lose contact with the ship. What the surviving astronauts eventually find is far more than the micro-organisms scientists currently hope might exist deep under the ice of Europa.
The film, by Ecuadorian director Sebastian Cordero, is now available on DVD and various internet film services. If you enjoy somewhat complicated but scientifically reasonable space stories, I commend it to your attention. If not, spend a little time Googling other images of Europa and check out one of the strangest worlds with which we have the pleasure of sharing the solar system.
Wednesday, June 18, 2014
Astronomers working with the Herschel space observatory have discovered water vapor coming from the largest asteroid in the asteroid belt, the one called Ceres (pronounced like "series"). By strict definition, Ceres is so big and round that it is no longer considered an asteroid, but is now designated dwarf planet number one (having been discovered on Jan. 1, 1801, long before Pluto).
Ceres is about 600 miles across and takes 4.6 years to orbit the Sun (Mars takes 1.9 years, while Jupiter takes 12 years.) The Hubble Space Telescope images of it (see one attached here) show lighter and darker areas. The water vapor is not evenly distributed around Ceres and there is more of it when Ceres is closer to the Sun, so there may be some ice that is sublimating (going from frozen form to vapor) in parts of Ceres.
At Ceres' distance from the Sun, ice on the surface would have all sublimated long ago, so this must be vapor coming from a deeper (frozen) layer, which was a surprise. Some astronomers think there may be enough water ice under the surface of Ceres to make an ocean. This is the first time water vapor has been detected in the asteroid belt, although we have seen it coming from a moon of Jupiter's and a moon of Saturn's. There may be plumes or "geysers" of water vapor coming from parts of Ceres, perhaps like the ones on Saturn's satellite Enceladus.
We will know a lot more about conditions on Ceres next March and April, when the Dawn spacecraft arrives for a rendezvous with Ceres and provides images with unprecedented detail of this intriguing member of our solar system. (Dawn gave us lots of great information about Vesta, the second largest asteroid, before it departed for Ceres in 2012.) Isn't it great how nature continues to surprise and delight us as we explore our cosmic neighborhood?
Sunday, June 8, 2014
Click on the photo to make it bigger ^
What we are actually looking at is a small part of a larger region where star birth is going on right now. Known by its catalog number of IC1396, this "emission nebula" is set to glow by the brilliant light of new stars that have already been born in this region and are shining with adolescent energy.
IC1396 is a cloud of loose gas and dark dust (the dust really isn't that different from what you find under your desk when you are too busy thinking cosmic thoughts to clean up regularly.) The dust is shaped into long filaments, when the light of energetic stars pushes the less dense parts of the dust away from the stars (in this case, in the down direction on this photo.) Only the thickest regions of dust remain after a while, making long, dark tendrils like we see here.
IC 1396 is about 3000 light years away in the constellation of Cepheus. You can see the entire nebula (much larger than the small part seen in our photo) here:
So what did the dark shape remind YOU of?
Monday, June 2, 2014
In the last couple of weeks, astronomers have announced the discovery of two stars that show evidence of having eaten some of their own Earth-like planets. Today came the announcement of the discovery of a star with planets that is growing larger and larger and is going to be eating its inner planets in the next couple of hundred million years.
These kinds of star "cannibal activity" are not that rare and should not cause us undue distress. It's business as usual in the Milky Way Galaxy, but what's new is that we are getting direct evidence for activities that earlier we only predicted from theory.
The two stars that already finished their meal a long time ago are known by their catalog numbers, HD20781 and HD20782. These stars belong to the same star system, and formed from the same original cloud of cosmic raw materials. This is the first "binary star" system where astronomers have discovered planets around each star. One has two Neptune-sized planets close by, the other has a Jupiter-sized planet whose orbit is not a nice circle but a stretched oval-shape.
Astronomers took a look at what the two stars are made of -- something we can learn by looking at the details in the colors of light from them. Every different element leaves its own "fingerprints" in the colors of light. Because the two stars formed at the same time, from the same "cosmic womb," we have more information about what they were like at the beginning.
According to Trey Mack, of Vanderbilt University, a graduate student who did the detailed analysis, both stars show evidence of elements in their atmospheres that were most likely not there when the two stars formed. Instead they are tell-tale signs of the stars having eaten planets made of rock. One star seems to have eaten the equivalent of 20 Earths, while the other consumed "only" ten Earths earlier in its history.
Astronomers have thought for a while that big "bully" planets like Jupiter and Neptune can, under the right circumstances, move inward and force smaller planets (like our Earth) to approach their stars until they are consumed. We are fortunate that this did not happen in the case of our solar system, and the Earth has a stable, undisturbed orbit which has allowed this blog's readers to evolve here. But it's getting clearer and clearer that not all star system will have the same history as ours did.
The other work deals with an act of cannibalism that happens late in the life of a star. All stars, at some point, have a "life-crisis" when their first fuel for making energy is all used up and the star has to adjust by briefly swelling up into a red-colored giant. The news is that astronomers have discovered that one of the stars around which the Kepler space mission has found three planets is on its way toward this period of swelling up. The star is known as Kepler 56, and the way in which it has started to swell up is telling us that it will eventually swallow its two inner planets, leaving only its outermost planet as survivor.
The devastation will not occur until more than a hundred million years have gone by, so it's not an immediate tragedy. We have seen many stars that swell up like this, but none of them have been known to possess planets. Kepler 56's worlds are therefore the first planets known to be orbiting other stars whose doom we can now predict. (By the way, in case you are worried, our own Sun will also have such a crisis and will swell up. But this is not happening for another five or six billion years, so I am not ready yet to include this eventuality on my home insurance policy.)
The image, by the way, is an artist's impression of an Earth-like planet being torn apart and then "eaten" by a Sun-like star.