Thursday, December 31, 2015

Pluto Stamps to Debut in 2016

The U.S. Postal Service is going to release the set of two Pluto and New Horizons stamps in 2016 that you see pictured here. There has been an interesting connection between stamps and the Pluto mission.
In 1991, back when Pluto was still a planet, the U.S. issued a set of stamps showing close-up photos from space missions to all the planets except Pluto. The Pluto stamp was a drawing, and said "Not Yet Explored." This stamp so annoyed Alan Stern and and other astronomers who had been arguing for a Pluto mission, it gave them new energy to pressure NASA to approve a Pluto flight.
In 2006, just before New Horizons was launched, the scientists put one of those annoying stamps aboard the spacecraft and it was thus part of the mission that flew by Pluto last July. Having a U.S. stamp eventually leave the solar system amused the Postal Service people, and the new stamp of what Pluto actually looks like (with that nice heart shaped feature) is the happy result.
The Postal service is also planning to issue another set of stamps of the 8 planets (not including any pesky dwarfs this time) and a Star Trek commemorative series. See the full information at:…/postal-service-honors-nasa-planetary…
Happy New Year to Fans of the Solar System and Stamp Collectors Everywhere! May your heart find fulfillment in the year ahead, just like Pluto's did..

Sunday, December 6, 2015

The Best Picture from Pluto So Far

The New Horizons spacecraft, which flew by Pluto in July, is slowly continuing to send back the images and data it took. The latest batch contains some of the most detailed close-up pictures of Pluto we have ever seen and they are fascinating!
Let’s take a look at the most intriguing new picture for a minute. We are seeing the greatest detail the spacecraft cameras were capable of. In a scene about 50 miles wide, we can make out details as small as half a city block. We see the shoreline of the Sputnik plains (part of the giant heart-shaped feature that caught everyone’s attention on the early pictures.)
The “rocks” that make up the mountains in the upper left are made of water – which is harder than rock at Pluto’s freezing temperatures. Some of these mountains are more than a mile and half high, with some of their sides bright with ice and others coated in a darker material that we are still learning about. This darker material may fall out of the sky, when ultraviolet light from the distant Sun causes chemical changes in Pluto’s thin atmosphere.
Notice how abruptly and cleanly the mountain end and give way to the softer, nitrogen-rich ice that makes up the Sputnik plains. In that ice, you can see huge but subtle cell-like structures. What makes up and drives this cell-like structure is still being debated by astronomers. Material in and around these cells may be moving up or down, like the cells you see when you boil miso soup. (If you've never boiled miso soup, ask a Japanese friend to tell you about it.) Cold nitrogen and methane ice might behave similarly when it is heated by the slightly warmer insides of Pluto and the faint heat of the Sun.
In an earlier photo, you can see some dark hills poking up at the boundary between cells, so this is very complicated terrain we are looking at. See the picture below. 
But just enjoy looking at the alien vista New Horizon’s cameras revealed. Pluto is not simple or boring!

Sunday, November 29, 2015

SETI Institute Searches for Giant Alien Construction Sites (and Your Support)

The team searching for signals from intelligent civilizations among the stars at the SETI Institute recently turned its radio telescopes to a mysterious star whose light output varies in an unusual way.   Called by its catalog number KIC 8462852, the star is about 1500 lightyears away in the constellation of Cygnus the Swan. Observations with the Kepler space telescope had shown that the star’s brightness dipped at irregular intervals and with irregular amounts of darkening.

Such dips are how the Kepler telescope finds planets orbiting distant stars.  Astronomers photograph huge numbers of stars regularly, and search for regular dips in a star’s light when a planet gets in front of the star, reducing its brightness.  A planet circles its star regularly, and the dips in brightness come on a clockwork schedule.  If the planet takes 100 days to orbit its star, astronomers would see a dip in brightness every 100 days – just while the planet is in front of its star.  Here is a little animation to show you the idea:

But KIC 8462852’s dips in brightness are not regular at all and they vary in how much of the star’s light they block.  One such dip in brightness took away more than 20% of the star’s light, indicating that whatever was causing it must be much bigger than a planet.  What could be causing such unpredictable and large dips?  It could, for example, be a huge swarm of comets that orbit the star in different clumps.  It could be great clouds of dust from deep space which the star happens to be moving through.  But there is another possibility, which got some astronomers and all science fiction fans excited.

What if there is an advanced civilization around that star, far beyond our own in technology?  One thing such a civilization is likely to need is huge amounts of energy to carry out their projects.   An easy way to get that is to build huge “solar panels” orbiting their star.  Alternatively, perhaps they are building giant space habitats to house their excess population. 

Just like our cities are irregularly spaced and irregular in terms of internal construction, so these space construction projects could be different in size and spacing, causing the irregular dips we see as they move in front of their star.  While the explanation is most likely something natural in the universe, it’s fun to consider a cause that could be a signal for the existence of intelligent life.

The leading organization in the search for life beyond Earth is the SETI Institute (where I have the privilege of serving on the Board of Trustees.)   They have an instrument, called the Allen Telescope Array (ATA), with 42 coordinated radio telescopes in Northern California, specifically designed to find intelligent radio or microwave signals from the stars.

For more than two weeks, the Institute team, led by Dr. Seth Shostak, trained the ATA on KIC 8462852, to see if any pattern of signals might be leaking from such an advanced civilization.  At a distance of 1500 lightyears (where each lightyear is 6,000 billion miles), the alien transmissions would have to be awfully strong to be detectable from Earth.  Still, a civilization able to build huge space structures might have powerful beacons to communicate with its own outposts, and we might be able to eavesdrop on one of their messages pointed our way.

So far, in the channels the Institute team searched, no intelligent signal was detectable.  They also searched for a much broader beam of microwaves, which advanced aliens might use to push giant ships through space.  No such beam was found either.

But what exciting ideas such observations bring to our minds!  The possibility of detecting some kind of intelligent species that is out there in the Galaxy has intrigued humanity for centuries.  Today, for the first time, we actually have the technology to do experiments in this area.  I’d love to see us find evidence that we have “cousins” among the stars.  This is why I have served on the SETI Board for many years now.

The Institute also does other wonderful research, in many areas of astronomy and planetary science.  (One of our scientists, Mark Showalter, found two of the small moons of Pluto, for example.)  There is also great work going on in education and public outreach, including the syndicated “Big Picture Science” radio show that Seth Shostak co-hosts.

December 1 is “Giving Tuesday” – a day designed for all of us to pause after the shopping frenzy that follows Thanksgiving, and consider giving to non-profit organizations whose work we believe in.  Perhaps you’d like to join me in supporting the SETI Institute.  For ways you can help, see their website at:

(NOTE: The photo shows a few of the radio telescopes that make up the Allen Telescope Array.)
And KIC stands for Kepler Input Catalog.

Sunday, November 22, 2015

Hot Discovery: Venus-like Planet around Red Dwarf Star

A newly discovered planet is as hot as your oven at full strength and takes less than two days to orbit its star.

As the number of confirmed planets orbiting other stars nears 2000 (when just twenty years ago, that number was zero), we are finding many planets that are not like any we know in our own solar system. The new planet orbits a red dwarf, a star 200 times fainter than our Sun, called GJ1132. (GJ stands for Gliese-Jahreiss, the name of two German astronomers who produced a remarkable catalog of the stars closest to our Sun.)

Astronomers used telescopes around the world to pin down the characteristics of the new planet, which is just 39 light years away, very close by cosmic standards. It turns out to be a rocky planet, a little bigger and more massive than Earth.

But it is so close to its star it takes only 1.6 days to go around. (In other words, a year on that planet would be just 1.6 Earth days. That means an Earth 10-year old would be about 2280 years old on that planet!)

At so close a distance (only a million and a half miles away from its star), the planet experiences temperatures on the order of 450 degrees Fahrenheit. So it reminds us more of superhot Venus in our solar system than our own Earth. Interestingly, other planets known to be rocky that we have discovered orbiting other stars are even hotter. (Hot, close planets are easier to find, so they are over-represented among our early discoveries.)

Still, if for some reason, you need a turkey cooked really fast this week, perhaps a quick trip to GJ 1132b (as the planet is boringly designated) would be in order. Or just give thanks that you live in a cooler planet which takes its time orbiting the Sun.

[P.S. The image is just an artist's impression. We can't photograph such small close in planets -- they are lost in the glare of their star.]

Monday, November 9, 2015

Pluto Has a Crazy Tumbling Moon (Great Video)

Pluto has five moons around it and one of them, it was reported today, spins 89 times for each orbit it makes around Pluto. Hydra, the outermost of Pluto's four tiny moons, takes 38 Earth days to go once around the dwarf planet. During that time, it rotates 89 times.

For a hypnotic video of the motion of all the moons, see:…/defau…/files/dps-slides-showalter1.mp4

(Note that on the video, the moons are not to scale. In real life, the outer 4 moons are much much smaller than Pluto and the giant inner moon Charon, which is about half of Pluto's size. But the motion you see on the video is real.)

Hydra is the purple object on the video. The moon colored yellow, called Nix, spins almost fourteen times during one of its orbits. (The colors mean nothing on the video; they just help our eyes tell the moons apart.)

Astronomer Mark Showalter of the SETI Institute, who discovered two of the moons, is part of a team that suspects that the tumbling of the moons is caused by the extra pull that the giant moon Charon adds to the pull of Pluto in this system.

Another interesting fact about the motions in the Pluto system is that Pluto's day is equal to Charon's month.  In other words, Pluto rotates at the same rate as its giant moon orbits it.  That means Pluto and Charon are synchronized -- one side of Pluto always has Charon above it as it turns, and the other side of Pluto never sees Charon.  

By the way, it also appears from the New Horizons data coming back to Earth that Hydra and Kerberos (the green colored moon) are each made of two smaller chunks of ice that "merged" into one close system early in Pluto's history. Perhaps all four of the small moons are the result of such mergers. So here are two chunks of cosmic material living together intimately for billions of years. Perhaps the Tea Party fundamentalists and Supreme Court Justice Scalia might not approve of such a "marriage" between icy chunks, but I think it's pretty cool.

Sunday, November 1, 2015

We Fly Through the Geysers Coming from Saturn's Moon

Last week, the Cassini spacecraft flew through the water geysers spurting from Saturn's mysterious little moon, Enceladus. NASA's steered the spacecraft to within 30 miles of the moon's surface and through the salt-water vapor that's coming up through the cracks of the moon's icy surface. How great that we can still maneuver the Cassini probe to do this after 11 years of orbiting Saturn!

Planetary scientists believe that there is likely to be an ocean of liquid water under Enceladus' crust. (The name, by the way is pronounced "En - salad - us," not as hard as it first looks.) You can see some of the deep cracks through which the water emerges in the foreground on our top image. Below is a drawing of how scientists imagine the moon's structure could be arranged inside.

We will know more about what the plumes are made of when the data are analyzed in coming weeks. Even from further away, previous flyby's have already identified some of the most basic chemicals that are the earliest building blocks of life in the plumes.

How a small frigid moon way out where Saturn orbits -- a moon only 300 miles or so across -- can have an underground ocean and geysers is still a puzzle, but it shows us that we should not take even the smaller moons in the outer solar system for granted.

As always, you can see the pictures in more detail if you click on them.  For more information on the Cassini mission, see: 

Sunday, October 18, 2015

My First Science Fiction Story Published

As some of you know, I have long enjoyed science fiction, both as fascinating reading and also as a nice addition to my introductory astronomy classes. For 30 years, I also kept a diary of science fiction ideas that occurred to me, and might make the basis of good stories.
In the last year or two, I have joined a writing group and am trying to create some SF short stories of my own. I have a full bulletin board of eloquent rejection slips from some of the finest science fiction magazines in print (as, I gather, all beginning writers must collect,) But now, one of my stories has been published, in a Mars-theme anthology called "Building Red," from a small independent press in St. Louis called Walrus Publishing (and the book is available on Amazon:…/…/1940442079 )
The story, based on a real discovery about Mars, takes place in part inside a cave on the flanks of one of the four giant volcanoes on Mars' equatorial bulge. Instead of the sanitized, squeaky-clean NASA version of a future Mars colony, I tried to imagine one that's crowded, smelly, and has its share of loners and misfits.
The story is entitled "The Cave in Arsia Mons" and it appears together with Mars stories by a number of writers, some of whom have a longer publishing record in SF than I do.

More generally, for a topical index to science fiction stories that have good astronomy in them, see my web page at: 

Sunday, October 11, 2015

Blue Skies on Pluto

The New Horizons team just released a great new image of Pluto in front of the Sun. If Pluto had no atmosphere, it would just have blocked the Sun's light for the camera. But Pluto's thin (but significant) atmosphere scatters blue light more than red, just like Earth's air does, and so we can glimpse blue skies (or at least blue haze) around Pluto in the picture.

The haze layers in Pluto's atmosphere (seen more clearly in the black and white photo below) are made of slightly larger particles than Earth's haze layers, a kind of alien soot.

The lower image, showing Pluto at sunset, shows how the haze has several layers in it. The atmosphere is a thin mixture of nitrogen, carbon monoxide, and methane. Not a place where you want to (or can) take a deep breath! Astronomers think the atmosphere of Pluto is a bit thicker when it's closer to the Sun in its 250-year orbit, and then freezes out when it moves away from the distant sun for most of its plutonian year.

Also on the lower image, you can see the contrast between the mountainous higher lands on Pluto, and then in the middle of the picture, the smoother frozen plains that interrupt them. Only about 10% of the images and data have been sent back by New Horizons so far, so we have much more to learn about the little planet we visited briefly in July.

(As always, click on the photos, to see more detailed versions. Feel free to pass the pictures and information on, if you like them.)

Sunday, October 4, 2015

"The Martian" and Other News of the Solar System

If you've seen, read, or heard about "The Martian" film or novel, you may know that it's a story by an engineer about survival on Mars. If you'd like some background on how author Andy Weir tried to make the story realistic, using known science, check out his talk at NASA's Ames Research Center at:

The image accompanying this post is a selfie of a real "martian" -- the Curiosity Rover on Mars, which took the pictures from which this great Mars image was assembled in August. If you click on the picture, you get a bigger version.

For a listing of other Mars science fiction stories with reasonable astronomy, you can download my one-page resource guide at:

A fantastic new image and movie of Pluto's giant moon Charon (with its mysterious red polar cap) can now be seen at: 

For those of you who are in the Northern California area, or have friends there, there are two exciting events coming up this week:
1) Dr. Carolyn Porco, the head of the imaging team for the Cassini mission at Saturn, is giving a free public lecture (with fabulous pictures) at Foothill College Wednesday night:

2) The Astronomical Society of the Pacific and Chabot Space Science Center are sponsoring an all-day Family Astronomy Festival in Oakland Saturday Oct. 10. See:

Sunday, September 20, 2015

A Total Eclipse of the Moon Sunday Evening September 27

I thought you might like advance notice of a very nice upcoming lunar eclipse visible next Sunday evening in North and South America and in the early morning in Europe and parts of Africa and west Asia. Below are the basics in the form of questions and answers.  All you need to enjoy the eclipse is clear skies and (on the American west coast) an unobstructed view toward the East.

Next week you will start reading media reports about this being both a “blood moon” and a “supermoon,” but don’t pay too much attention to that.  The Moon will be a bit closer to the Earth in its orbit than average, making it look a bit bigger, but the difference is not especially significant.  And every lunar eclipse could turn reddish, as explained below.  It’s rarely the color of blood, but the media love anything that can be connected to thoughts of violence.

The Sept. 27, 2015 Total Eclipse of the Moon

1. What Is Happening?

On Sunday evening Sept. 27, a total eclipse of the Moon will be visible from throughout the U.S. (and North and South America.) In a lunar eclipse, the full Moon & the Sun are exactly opposite each other in our sky, and the Earth gets between them. This means the Earth’s shadow falls on the full Moon, darkening it.  It’s a nicely democratic event; no special equipment is needed to see it (provided it’s not cloudy or foggy.) Plus it happens early in the evening; kids can watch & still be awake for school next day.

2. When Will the Eclipse Happen?

The table below is for the U.S. (for other countries and continents, see:  which can be set for your home location.) 

Partial eclipse starts
Moon not up
7:07 pm
8:07 pm
9:07 pm
Total eclipse starts
7:11 pm
8:11 pm
9:11 pm
10:11 pm
Total eclipse ends
8:23 pm
9:23 pm
10:23 pm
11:23 pm
Partial eclipse ends
9:27 pm
10:27 pm
11:27 pm
12:27 am

As Earth’s shadow slowly moves across the Moon, we first see only part of the Moon darkening (partial eclipse).  When our shadow completely covers the Moon, we see a total eclipse. The best time to start watching is about a 20 minutes before total eclipse begins, when much of the Moon is already darkened. 

NOTE: On the west coast, the eclipse will start low in the Eastern sky, so make sure your observing location has an unobstructed view toward the Eastern horizon.

3. What is Visible During a Lunar Eclipse?

As the shadow of the Earth covers the Moon, note that our natural satellite doesn’t become completely dark.  Some sunlight bent through the Earth’s atmosphere still reaches the shadowed Moon and gives it a dull brown or reddish glow.  The exact color of the glow and its darkness depend in part on the “sooty-ness” of our atmosphere – how recently volcanoes have gone off and how much cloud cover, storm activity, and human pollution there is around the globe. 

Once the Moon is totally eclipsed, the stars in the sky should become more easy to see.  What makes this eclipse a little bit unusual is that, by coincidence, it is happening just one hour after the Moon has reached the closest point in its monthly orbit around the Earth.  So the Moon will look a bit larger in the sky than usual.  (The media will be calling it a “supermoon,” but the effect is pretty subtle for the average person.)

4. Is it Safe to Watch, and How do I Watch?

Since the Moon is safe to look at, and eclipses make the Moon darker, there’s no danger in watching the eclipse with your eyes or a telescope.  (The dangerous eclipse is the solar one, where it is the Sun that gets covered.) And lunar eclipses don’t require you to go to a dark location.  Bring binoculars to see the Moon larger, but just your eyes are fine.  Since the total eclipse will last for an hour and 12 minutes, be sure to take someone along with whom you like to spend time in the dark!

5. What Can I Tell My Kids (or Kid Brother or Sister)?

Suggest that they take a careful look at the shadow of the Earth as it moves across the bright face of the Moon.  What shape is it?  The round shape of the Earth's shadow suggested to the ancient Greeks, more than 2000 years ago, that the Earth’s shape must be round too.  Eclipse after eclipse, they saw that the Earth cast a round shadow, and deduced that we lived on a round planet (long before we had pictures of it from space.)

Sunday, August 30, 2015

Two Giant Black Holes Whirl at the Core of an Active Galaxy

Using the Hubble Space Telescope, a team of astronomers has found that a superbright (active) galaxy is powered at its core by two supermassive black holes whirling around each other in only a bit more than one year. This remarkable galaxy is called Markarian 231, after the Armenian astronomer who made a catalog of such active galaxies (with unusually bright centers.)
The galaxy is almost 600 million lightyears away, so we cannot see the tiny area in the center which contains the black holes directly. But a detailed study of the ultraviolet light from the core of the galaxy strongly implies that a black hole containing enough material to make 4 million Suns is whirling around a much larger black hole (with mass inside for 150 million Suns.)
Think about those numbers! You would not want to live near such overweight black holes, but luckily they are confined to the central regions of galaxies (including our own Milky Way) and are not a feature of the galactic outskirts where our solar system resides in comparative peace.
The idea that enormous black holes like this can share the same environment is not news to astronomers, but it's nice to have such a clear example. We now know that the giant islands of stars called galaxies probably all started much smaller and have been growing through "mergers" (if you'll pardon our appropriating a word from the world of business.)
Smaller galaxies are "eaten" by larger ones, or two galaxies of equal size are attracted together by their mutual gravity. If the smaller galaxies each contain a big black hole, both black holes will wind up near the center of the merged object. If the original galaxies had orbiting motion around each other, their inner black holes will have some of that motion, and can circle each other until -- later -- their gravity also pulls them together.
The fact that the two black holes in Markarian 231 take only about one year to go around means they will collide in a few hundred thousand years (a long time compared to the presidential nomination season, but short for galaxies.)
When two black holes collide you get -- surprise, surprise -- a bigger black hole. But we have caught Markarian 231 in the act of a small galaxy having been swallowed, but before the two black holes had time to merge. There are stars and huge clouds of gas and dust being pulled in by the pair of black holes and as they are torn apart and whirled around, they give off a lot of energy.
It's that energy of doomed material (before it falls into one or the other black hole) that makes Markarian 231's center so unusually bright.
The method used to find the waltzing, whirling black holes in this galaxy holds promise for finding other pairs of giant black holes in other distant galaxies. And the existence of such pairs of hungry black holes is good evidence that our merger theory of how galaxies "bulk up" is correct.

(By the way, our image, above, is a painting, based on the Hubble data.  As we said, we can't take a picture of the inner part of the galaxy.  But below is a Hubble image of the entire disturbed galaxy with its bright center.)

Sunday, August 9, 2015

Good Meteor Shower This Wednesday Night

This Wednesday evening and Thursday morning there will be one of the best meteor showers you and your family can see.

This is a great year for the Perseid meteor shower, because it is happening during the phase of the Moon called New Moon (which is when the moon is absent from the sky).  So there will be no moonlight to interfere with seeing the faint “shooting stars” of the meteor shower.

The best night is the evening of Wed, Aug. 12 and morning of Thur., Aug. 13, although there could be significantly more meteors on the night before and the night after too.  Meteors (which have nothing to do with stars) are pieces of cosmic dust and dirt hitting the Earth’s atmosphere at high speed and making a flash of light.

The peak of the shower is predicted to happen around 1 am PDT Aug. 13th, which means that after it gets dark on Aug. 12th, there should already a good number of meteors to watch for.

Here are a few tips for best viewing:


1. Get away from city lights and find a location that’s relatively dark
2. If it’s significantly foggy or cloudy, you’re out of luck
3. Your location should allow you to see as much of the dome of the sky as possible
4. Allow time for your eyes to get adapted to the dark (at least 10 -15 minutes)
5. Don’t use a telescope or binoculars – they restrict your view (so you don’t have to be part of the 1% with fancy equipment to see it; this is a show for the 99%!)
6. Dress warm – it can get cooler at night even in August
7. Be patient (it’s not fireworks): keep looking up & around & you’ll see flashes of light
8. Take someone with you with whom you like to spend time in the dark!

The Perseid meteors are cosmic “garbage” (dust and dirt clumps) left over from a regularly returning comet, called Swift-Tuttle (after the two astronomers who first discovered it).  The comet itself returns to the inner solar system every 130 years; it was last here in 1992.  During each pass it leaves dirt and dust behind and it is this long dirt and dust stream that we encounter every August.  Some experts are predicting we might briefly encounter an especially crowded part of the debris stream this time.

Each flash you see is a bit of material from the comet hitting the Earth’s atmosphere and getting heated up (and heating up the air around it) as it speeds through our thick atmosphere.  Both the superheated dust and dirt and the heated air contribute to the visible light we observe.  Since comets are left-overs from the early days of our solar system, you can tell yourself (or your kids) that each flash of light is the “last gasp” of cosmic material that formed some 5 billion years ago.

[Note: image from Mike Hanley, American Meteor Society]

Sunday, July 26, 2015

New Pluto Images Reveal Glaciers Flowing from the Heart

New images released from the New Horizons spacecraft's encounter with Pluto reveal a reddish world, where water is as hard as rock, and substances that are gas on Earth have become ice glaciers. The beautiful color picture with this post shows you a section of Pluto that includes the heart-shaped feature named after Clyde Tombaugh, Pluto's discoverer. The left lobe (section) of the heart is being called the "Sputnik region," after the first satellite humanity ever sent into outer space.
Why is Pluto reddish? The team's first thought is that ultra-violet light from the Sun acts on the gases in the thin Pluto atmosphere -- methane (natural gas) in particular -- and breaks them apart and reforms them into more complicated combinations of hydrogen and carbon. Eventually, the molecules get so complex and heavy, they fall out of the air and coat the surface. Such hydrocarbons tend to be reddish when we see them on other worlds.
The New Horizons craft has only returned about 5% of the data it has stored in its memory, but even first results show haze layers in the Pluto atmosphere that support the notion of the air having chemical reactions going on, despite the cold.
If you look at the Heart in the picture, you can see that the left Sputnik region (which is about the size of Texas) has a thicker covering of ice than the right half of the Heart. Our black-and-white image shows a close-up about 250 miles wide in the northern part of Sputnik. At the top you see some of the older, cratered terrain that is above the Heart. But below that, the Heart itself is smooth and young-looking (no craters, which are a sign of age.)

The smooth ice we see is made of nitrogen, methane, and carbon monoxide, its top layers freezing out of the air when Pluto gets further from the Sun. (Pluto was closest to the Sun in its almost 250-year orbit in 1989, so we are just moving away from the time that Pluto is warmest.)
At Pluto temperatures, an ice made of nitrogen will very slowly flow, like a glacier flows across the landscape on Earth. The arrows on our black-and-white image show the direction scientists think the ice is flowing in Sputnik. At Friday's press conference, the experts said that their impression of Sputnik is that it's a very young region (geologically speaking) -- perhaps only tens of millions of years old. (For comparison, we think Pluto, like the rest of the solar system, is 4600 million years old.) Its glaciers have moved into any available regions next to Sputnik, and have filled valleys and craters on all sides.
Look also at the intriguing "polygon" patterns (many-sided figures) in the ice of Sputnik on our picture. They look like huge, geometric cells in the ice, perhaps half a mile or more deep. One possibility is that in these cells, hotter material from deeper inside is slowly rising, a process called "convection."
These images and ideas are just the (pardon the expression when discussing Pluto), just the tip of the iceberg. It will take 16 months for the full set of pictures and data to be sent back from New Horizons. Better images are expected in September, for example. Stay tuned.

In this last image, you see Pluto (left) and its large moon Charon in realistic color.  Such a dramatic pair at the outskirts of our solar system!

Friday, July 17, 2015

Getting Close-up with Pluto's Moon Charon

One of the most intriguing things about Pluto is that it is more of a double planet than a planet with moons. One of Pluto's moons, Charon (pronounced like Sharon or Karen; both are used) is half the size of Pluto. No other moon we know is this big compared to the planet it orbits -- just another way that the Pluto system operates outside the usual rulebooks.

The diameter of Charon has been measured to be 751 miles, about the size of Texas. Charon has settled into the most comfortable orbit around Pluto that nature permits. It rotates and revolves in 6.4 Earth days, which is also the rate at which Pluto turns. This means that the day on Pluto is the same length as the Charon month, which hurts your head if you try to think too much about it.

Now the New Horizons craft is starting to send back images of Charon as well, and again, we are surprised. Our photo shows a black and white global picture of Charon that has been tinted with actual color information from one of the other instruments. The New Horizons team is informally referring to the striking dark spot near the top of the image as "Mordor," much to the delight of fans of the Lord of the Rings trilogy.

But the inset in our picture is the most interesting. It shows an area of about 240 miles across (from top to bottom) and you can see some of the trenches and canyons that we are finding on Charon. Craters are also visible. Near the top left, we see a giant ice mountain sticking out of a trench. The NASA news release says: “This is a feature that has geologists stunned and stumped.” How did the mountain get or grow in there? It's those kind of odd mysteries that scientists live for.

(By the way, if you were asking yourself why the big moon has two different ways of pronouncing its name, it's a romantic story. The proper pronunciation from Greek mythology is like "Karen". But James Christy, the astronomer who discovered the big moon in 1978, secretly wanted the name to also remind people of his wife Charlene. So he likes making the name sound more like "Sharon." Astronomers (like most people) love romantic stories, so many use the pronunciation that Christy likes.

And Pluto itself has a name with a secret -- the astronomers at the Lowell observatory wanted to name it after their patron and founder, Percival Lowell, but we don't name planets after real people. So when a schoolgirl in England suggested the name Pluto to them, they jumped at it, since the first two letters are Lowell's initials.)

Wednesday, July 15, 2015

First Close-up Peek at Pluto's Surface

Here is the first detailed image of the surface of Pluto, released today, and it's already providing surprises. The yellow bar gives you a sense of scale; Pluto's diameter is 1473 miles (just measured by New Horizons), so we are seeing only a small part of it here.
The angular structures in the top half of the picture are mountains, the tallest being about 2 miles high. Most likely these mountains are made of frozen water -- it's so cold on Pluto that water becomes harder than rock. In fact, it is likely to be layers of "hard frozen water" that make up much of the surface of this distant world.
The biggest surprise is that the surface shows no craters, large or small. Craters are made on every world when chunks of rock or ice hit and carve out a circular depression. Since every world is regularly being hit by pieces of cosmic debris that fly through our solar system, any world without craters must have a way of erasing them pretty quickly after they form. Scientists are estimating that the absence of craters means that the surface of Pluto is being refreshed by some process, and can't be more than a hundred millions years old -- which is very YOUNG compared to the 4600 million year age of the solar system. What keeps the surface of this little world refreshed and erased is the first challenge Pluto has thrown in the face of the scientists eager to study it.

Sunday, July 12, 2015

The Revenge of the Dwarf Planets

Pluto Seen July 11, 2015 from NASA's New Horizons Spacecraft

This coming Tuesday, July 14th, humanity will -- for the first time -- fly by the world formerly known as planet Pluto.  Actually, the New Horizons spacecraft will be flying by a double world, because Pluto has a giant moon, Charon, which is half its size.  I can't wait to see the pictures.

In fact, see the Pluto image with this post -- it's from yesterday and already shows intriguing spots and circular areas.  Check out the even better new pictures and information as they are revealed this coming week and month.  You can find them at: 

When the data from the flyby are returned to Earth -- and they will take a year to download (and you think your connection is slow!!) -- we will have completed our first-look exploration of all the main worlds known when most of my readers were born.

Pluto was "kicked out of the planet club" only because a whole bunch of other "Plutos" were found beyond Neptune.  Pluto turned out to be the first of its kind (found by Clyde Tombaugh at Lowell Observatory in 1930), but now we've found Eris (which is the same size as Pluto) and several other round icy worlds that are smaller versions of them.  We probably should have picked a less insulting name than dwarf planet, but we used the word dwarf successfully in combination with star and galaxy, so we didn't anticipate so much public hostility to it.  For the full story, see: 

A few of Clyde Tombaugh's ashes are aboard the New Horizons craft.  You can read his own story of the discovery at:

Here is Clyde Tombaugh with your friendly blogger in 1985

Pluto is known to have four smaller moons, and others may yet be discovered in the coming weeks.  Pluto also has a thin changeable atmosphere, which instruments will be investigating as we fly by.

Another world that got reclassified in the Pluto saga was Ceres, the largest asteroid, which is now also called a dwarf planet.  Ceres is the only member of the asteroid belt between Mars and Jupiter to be round.  The Dawn spacecraft is settling into a lower and lower orbit around Ceres this summer and fall, and will be sending back never-before-seen details of what this intriguing world (about the size of Texas) looks like.

So it's going to be a summer of dwarf planet discovery.  They are going to be in the news so much, maybe we'll forget the issue of the name and enjoy them for what they have to tell us about the history and diversity of the solar system.

If you are really into the Pluto encounter, the most comprehensive post about what's happening is Emily Lakdawalla's at: 

Wednesday, June 17, 2015

Astronomers Find a Planet Like Mars in a Distant Star System

A team of astronomers has found the equivalent to planet Mars in a star system with three planets 200 light years away.  This is the planet with the lowest mass found so far around any normal star.  That’s because the methods that allow us to find the masses of planets (how much they weigh) generally work best for planets that are heavier.  Here a wonderful combination of circumstances allowed the team (including Jason Rowe of the SETI Institute) to make their record-breaking measurement.

The nameless star system is given the catalog designation Kepler 138, because the three planets, orbiting a cooler star, were first discovered by the Kepler spacecraft.  Kepler allows astronomers to find planets when they move across the face of their stars, causing a tiny eclipse (or “transit.”)  Tremendously accurate instruments aboard Kepler measured the decrease of light when each planet got in front of the star.

The three planets are each closer to their star than Mercury is to our Sun.  The planet that resembles Mars, closest of the three, takes only 10.3 days to go around.  In other words, a year on that planet is 10 Earth days.  Think how often you’d have to celebrate annual events, like your birthday!

The present team of astronomers (which also includes members from NASA’s Ames Research Center and Penn State) followed the three planets’ transits over time and noticed that they did not occur at the same time each orbit, because the gravity of the other two close planets was tugging on each one.  By measuring the size of the tugs, the astronomers could derive the gravity (mass) of each planet, something that is otherwise very hard to do.

Now here is the clever part.  When we watch a planet go in front of its star, that allows to measure how big the planet is (its diameter).  Bigger planets block more light.   So for these three planets, we now had the mass (from the tugs) and the size (from the transits).  Most of the time, when they find planets around other stars, astronomers only have one OR the other. 

Since we have both in this case, that allows us to calculate the density of each world. If a planet is dense, it is likely to made mostly of rock, like Earth is.  If a planet is not so dense, it combines rock with ice or even perhaps melted ice, such as the liquids we find inside Jupiter and the other partly liquid planets in our solar system.

This is what allowed the team to say with some certainty that the inner planet in the Kepler 138 system is about the size of Mars and about the same composition as Mars.  The planet is roughly 10% the mass of Earth and half the size of Earth, just like Mars is.   This is the smallest world for which we have both size and mass.

Almost 2000 planets are now known around other stars, a remarkable number, given that the first one was discovered just 20 years ago.  What amazes us is the variety of planets out there.   There are huge planets, bigger than Jupiter, but orbiting very close to their stars.  There are planets we are calling super-Earths, that are intermediate in size between Earth and Neptune.  And now we know that there are smaller, solid worlds like Mars.  Some smaller worlds are really close to their stars, like the one around Kepler 138, but others are much further out, like Mars is in our solar system.   Nature likes diversity in astronomical settings, much as she likes it for people.

(For a nice "infographic" about the Kepler 138 system compared with our solar system, see:

Sunday, June 7, 2015

Where Would Bill Gates' Great Granddaughter Go for Her Honeymoon?

Imagine a future when space travel is common-place and you can visit the planets.  What will be the top tourist sights in our solar system?  (This is an activity I like to have my students think about as they get near the end of my introduction to the planets class.)

If you are an astronomy fan, play the game yourself. What would you pick for those once-in-a-lifetime sights that future travelers may want to visit and photograph on a honeymoon trip or graduation journey?  

For those of you who happen to be in Northern California on Saturday evening, June 20th, I will be revealing my favorites in a free public talk on Mt. Tamalpais just north of San Francisco.  (My first-ever outdoor lecture with slides!)

For those elsewhere, I'll give you a sample.  Some of my favorite stops include the 4,000-mile lava channel on Venus (always a good planet for a hot time), the towering Mount Olympus volcano on Mars (three times the height of Mount Everest), the awesome Verona Cliffs on the moon Miranda (which are the tallest “lover’s leap” in the solar system), and the recently discovered steam geysers on Saturn’s intriguing moon Enceladus (nicknamed “Cold Faithful.”)

After the lecture, there will be a laser-guided tour of the night sky by Paul Salazar and stargazing through the telescopes of the San Francisco Amateur Astronomers. This is an OUTDOOR venue, so we ask that people dress appropriately (it can get cold), and bring a flashlight to help find your way to and from the parking lots.

Admission is free, but seating is on a first-come, first-served basis. 

If it looks like rain, please call the Mt. Tam hotline at 415-455-5370, after 4 pm.  Since this is an outdoor event, it gets canceled if it is raining.

Our photo shows Saturn casting a shadow on its own sunlit rings in a view from the Cassini spacecraft.