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.

Saturday, May 23, 2015

Mars Rover Sees Rock Spire as It Reaches 4000th Martian Day Record

At the end of April, the Opportunity Rover on Mars reached its 4000th martian day of operations! (A day on Mars is 24 hours and 40 minutes long.) Opportunity has been exploring the planets since early in 2004, and has survived far longer than most scientists and engineers expected.

Our photo shows a beautiful image mosaic it took of the red deserts of Mars, focusing on an elongated crater (seen a bit darker than the surrounding countryside) called "Spirit of St. Louis."

If you click on the picture, you can see it bigger. The crater is about 110 feet long and the interesting rock spire on its far end is about 7 to 10 feet high.

The Spirit of St. Louis crater is on the outer part of the western rim of a much larger crater that Opportunity has been exploring, called Endeavour. You have a view into that bigger crater if you look on either side of the rock spire.

(If the names in this story are not your favorites, you are not alone. Not everyone loves the NASA designations; I think not even Donald Trump would name his child Opportunity, but what are you going to do.)

Mars is every bit as dry and dusty as you might imagine from this picture. The energy for the stalwart little rover comes from its solar panels, and over the years they have become covered with dust. Each time, we thought this spelled the end of the mission, but then the martian winds whipped up a dust devil, which cleaned the solar panels and gave the rover fresh life. Planetary exploration is full of surprises.


For a different view, from a different robotic explorer, check out the small but fascinating mineral veins, seen by the Curiosity Rover in March, at:
The mineral rows we see are only about 2.5 inches high, but wonderfully complex.  By the way, this picture has been edited to change the martian light slightly to be more like Earth light, so geologists could compare the mineral deposits to more familiar ones on Earth. The picture you see is a combination of 28 telephoto lens images.  Aren't they wonderfully sharp?

Speaking of Sharp, Curiosity is now making its way toward and up Mt. Sharp, the layered mountain inside a crater which we think was under water billions of years ago. We expect lots of great images as Curiosity makes its slow and careful trek up the mountain.

Wednesday, April 29, 2015

First Movies of Pluto (Not Much Detail, But Still Amazing to Have)

Scientists working with the New Horizons spacecraft, which is scheduled to reach Pluto in July, released the first ever long-distance movies of Pluto and its giant moon Charon today.

The spacecraft was between 69 and 64 million miles away from Pluto when the images were taken, still roughly 3/4 of the distance between the Earth and the Sun. So these movies are very crude compared to what we will have soon.

Still, to have any real detail at all in our views of Pluto and Charon is wonderful and just whets our appetites for what's coming, as we get closer and closer to the famous dwarf planet that got so much public pity in the last few years. Discovered in 1930, it is (as the news release with the film says,) a cool mystery at the outskirts of the known solar system. But soon, thanks to NASA's long flight out there, we will know so much more about it. Stay tuned.

(If you click on the link, you will find two different perspective movies and some background information.)

Wednesday, April 22, 2015

The Search for Super-civilizations in the Cosmos

The WISE Telescope

In 1964, Russian scientist Nikolai Kardashev suggested that in the long history of the universe, which began billions of years before the origin of our Sun and Earth, really advanced civilizations might have developed.  Such civilizations might learn to control the total power of their stars -- and, ultimately, the total power of their galaxies. 

Now, Jason Wright and Roger Griffith, a pair of scientists at Penn State University, have actually searched for this last kind of super-civilization.  If such advanced beings have actually colonized and exploited the billions of stars within a galaxy, these civilizations could produce tremendous amounts of waste heat.  

Just like your car and your computer produce waste heat while they are operating, so the thought is that large-scale civilizations will generate an unnatural amount of heat, beyond the heat that all objects give off.

A recent satellite called the Widefield Infrared Survey Explorer (WISE) has been collecting information on sources of heat energy around the sky.  Wright and Griffith have looked at the output of 100,000 galaxies, to see if anyone of them might betray signs that the heat they produce is not natural, but comes from a super-civilization.

Although they did not find any obvious and definitive evidence, they did note some galaxies whose infrared energy was unusual in some ways.  These are worth investigating further. 

Of course no one really knows whether intelligent creatures can ever evolve to a level of technology where they take over an entire galaxy.  So finding one by this method is a long shot. (But I asked Geoff Marcy, the world's leading planet hunter, and he pointed out that just about all our searches for intelligence in the universe so far have been "long shots" -- no one can be sure today what method will pay off.  So Marcy feels we should explore as many different methods as possible.)

I also asked Jill Tarter, the U.S. leader of the search for extra-terrestrial intelligence using radio waves, and she also was excited about our adding more techniques to our SETI arsenal.  She told me she was adding the unusual galaxies from the WISE survey to the list of places where they would point radio telescopes, just in case there were any intelligent radio signals to be found.

Indeed, the SETI institute organized a Google hangout about this survey, and included Jill Tarter and Freeman Dyson, who first suggested ways that an advanced civilization might betray itself with infrared waves.  You can hang out and see what they said at:  

Sunday, April 12, 2015

A Monster Misses a Meal

There is a monster at the heart of our Milky Way Galaxy.  It's a super-massive black hole that has already eaten enough material to make 4 million stars like our Sun!  And, like all black holes, it is still hungry.  

For material to be "eaten" by a black hole, it must come quite close to the black hole "mouth" which astronomers call its event horizon.  Because black holes are the most compressed (squozen) objects in the universe, even overfed monster black holes have relatively small event horizons. Astronomers estimate that the one at the center of our Galaxy is 80 to 100 million miles across.  That's roughly the distance between the Earth and the Sun and is a tiny space in which to put 4 million(!) Suns.

So material near our black holes must come close to that tiny region to serve as food for the monster.  Things further away, like stars, can orbit around the black hole and not get swallowed.  (It is from the movement of such close, but not doomed, stars that we can estimate the gravity of the black hole.)

For the last few years, astronomers who monitor the center of our Galaxy have been predicting that a snack is on its way to the black hole.  A dusty cloud of material which they have nicknamed G2 was going to have a close encounter of the worst kind with the black hole in May 2014.  It was going to be torn apart by the enormous gravity of the monster and some of its material was then going to provide a meal for the black hole.  

When gas clouds (or other food) fall into a black hole, they are whirled around with unbelievable speed just before they fall in, and tend to glow briefly with x-rays and other forms of radiation before they disappear in the event horizon. However, no such flare-up of radiation was seen, even when the world's largest telescopes (like the Keck in Hawaii and the European Very Large Telescope in Chile). 

It appears G2 was not torn apart and consumed, because it wasn't a loose cloud of raw material, but a star with some of its birth material still around it.   The star managed to hold on to its "stuff" and make it away from the black hole, depriving it of a meal at this time.  Sorry, monster.   Better luck next time.

(In the picture, you see G2 in different colors going around the black hole (which is invisible, but whose position is marked by the plus sign.)  The blobs are shown at different times, and are red when G2 was moving away from us, and blue now that it was flung around the black hole and is coming toward us.)

Thursday, March 26, 2015

Einstein's Lens Splits Space and Time

This year, we celebrate the 100th anniversary of the first publication of Einstein's greatest masterpiece, the General Theory of Relativity.  Now astronomers using the Hubble Space Telescope have found a remarkable quadruple image of a distant exploding star which helps confirm another of that theory's most "far out" predictions.

The General Theory connects space, time, and gravity in mind-boggling ways.  Strong gravity can actually warp (or bend) space and distort the flow of time.  One example of gravity strong enough to do this is a dense cluster of galaxies, like the one shown on our image.  Everything on this Hubble picture that is not a point of light (everything with a shape) is a galaxy of billions of stars.  The cluster contains many such galaxies orbiting a common center. 

Light from more distant objects behind the cluster has to go through the strong gravity of the cluster on its way to us.  Einstein's theory predicts that as gravity warps space, the light from behind the cluster will have to travel through that warped space and will get twisted and bent in eerie ways.  From the right angle, a single beam of light can be split into four similar images, something called an "Einstein Cross."  That's just what you see in the inset on the picture.

Most amazingly, the four images of the exploding star took slightly different amounts of time to get to us through that warped space, and so we are seeing the same explosion at four different time periods.  By studying the details of such complex "gravitational lenses" (as the distortion by the galaxy cluster is called), astronomers hope to learn more about how all the "stuff" in those galaxies is distributed and how much of it is regular matter and how much is dark matter.

The galaxy cluster only has a catalog number, not a name, but we know it is about 5 billion lightyears away (meaning light, traveling at the fastest permitted speed in the universe, took five billion years to reach us.)  The exploding star appears to be four billion lightyears further than that -- meaning we are seeing its light from 9 billion years ago.  The only reason we can see it at all is that the gravity of the galaxy cluster actually intensifies the light as well as splitting it -- just as Einstein's theory predicts.  

What a wonderful image with which to celebrate the 100th anniversary of a theory that Einstein's called "the happiest thought of my life!"

(Click on the image to see it bigger -- believe me, it's worth it!)