Sunday, April 16, 2017

A Mini-Pluto at the Edge of Our Solar System

Astronomers have better measurements now of what is turning out to be a smaller version of Pluto located so far away that it may take 1,100 years to orbit the Sun. Nicknamed D.D. (or DeeDee) for Distant Dwarf, this remarkable small world appears to be about 400 miles in diameter -- only about 1/4 the size of Pluto, but possibly still big enough to be round like a planet.
D.D. was found in the fall of 2016 by a team of astronomers led by David Gerdes of the University of Michigan. As so often happens in astronomy, they were looking for something completely different, but found D.D. as part of their work. Now they have used an array of radio telescopes, called ALMA, to measure D.D.'s size and also to estimate its temperature. Ninety-two times as far from the Sun as the Earth is, D.D. is thought to be at minus 405 degrees Fahrenheit (minus 243 degrees Celsius; or only 30 degrees above nature's limit, absolute zero.)

D.D. is part of a whole zone of icy objects out beyond Neptune (astronomers call them Trans-Neptunian Objects or TNO's,) About 2,000 TNOs are now known, but most of them are too small and irregular (knotty potato-shaped) to be called dwarf planets. Pluto, the first TNO dwarf planet, was discovered in 1930, but in the last decade of the 20th century and the first decade of the 21st century, others were found, including Eris, Makemake, and Haumea. (If the names sound unusual, it's because we are trying now to name these outer worlds after mythological beings from many cultures, not just the ancient Greeks or Romans!)
We need more observations of D.D. before we are ready to call it a dwarf planet. If you thought that Pluto was being insulted when we called it a dwarf planet, perhaps it will help you to know that Pluto is the "first" of a whole new category of worlds. Five dwarf planets are now officially recognized by the International Astronomical Union, and at least six other worlds out beyond Neptune may eventually be included in the group. It may be years before we know if D.D. will join them.

But it's wonderful to see the Sun's family growing in this way, with our new instruments and surveys able to find worlds that literally are "far out!"

Sunday, March 26, 2017

Two Million Free Eclipse Glasses through Libraries (and a Free Booklet)

As you may know, there will be a rare eclipse of the Sun on August 21, 2017, and it will be visible throughout the United States. A spectacular TOTAL eclipse will be seen on a narrow path (about 70 miles wide) from Oregon to South Carolina. The rest of the U.S. and North America will see a PARTIAL eclipse, where only a part (but a substantial part) of the Sun is covered by the Moon. To look at the Sun when part of it is showing, special (but not expensive) glasses are required or you could damage the sensitive tissue in your eyes.
Millions of people will need glasses on August 21, and for the last year I have been grappling with the issue of how to get glasses to as many people as possible. Now, I am delighted to tell you that several astronomy colleagues and I have been able to get funding for glasses to be distributed through public libraries nationwide.
Thanks to the generosity of the Gordon and Betty Moore Foundation near San Francisco and Google, two million safe eclipse glasses will be made available through public libraries. Each library will get a supply of glasses to share free of charge and a booklet all about the eclipse and how to explain it to the public. The booklet, which I wrote with my colleague Dennis Schatz, is now ready and can be downloaded free at:
The first part of the booklet explains all about eclipses, the August eclipse and when and how it will be visible in different parts of the country, and how to observe it safely. It's written for beginners in science, so we hope everyone can benefit from it. The second part consists of information to help librarians plan public programs around the eclipse.
You could do your city or town a big favor by taking the booklet or just its web address in to your local library and encouraging them to participate in the eclipse and the glasses giveaway. Libraries can register for the program (through the STARNet Library Network at the Space Science Institute) at the website:
If, for some reason, your library can't participate in the program, there is information in the booklet on how to get eclipse glasses from the companies that manufacture the certified safe glasses that will protect you and your family's eyes. This spring is the time to make plans for where you will be and what you will do when the eclipse arrives on August 21.

Sunday, March 19, 2017

Bubbly Burp Tracks Giant Black Hole's Last Meal

Observations with a number of telescopes, including the Hubble, have now dated a kind of burp in the eating habits of the giant black hole at the center of our Milky Way Galaxy. It appears that about six million years ago, the central black hole "ate" a large cluster of stars and the neighborhood around it was energized by the process of the meal.

Black holes are regions where material (starting with dead stars) has collapsed so much, that nothing, not even light, can get out. The black hole at the center of our Milky Way now includes enough material to make more than 4 million stars like the Sun! It's what we call a "supermassive black hole" and lurks in the middle of our Galaxy like a giant speed trap for unwary stars or star groups that get too close.
As material is in the process of being "swallowed" by the black hole, it glows with desperate radiation, just before it falls in and disappears from view. A great bubble produced by the black hole as it ate its last serious meal has now been tracked by astronomers with much greater precision.
Just like the sound of the burp your uncle makes (after a heavy Thanksgiving meal) can travel through the dining room, so the bubble from this last meal can be seen traveling through the Galaxy like a giant expanding shell. The shell was probe by the Hubble as the light of distant objects raced through it and astronomers were able to measure the speed of the bubble's motion.
Six million or so years ago, it appears that a large clump of stars or gas (the raw materials of stars) was consumed by the black hole, making two "Fermi bubbles" in the Galaxy. Since then, the black hole has only been "snacking" -- tearing apart and eating an occasional star or random bit of gas. But no serious meal has made a big bubble from the mouth of the black hole since then.
Our diagram shows how in the six million years since that meal, the bubble has expanded at speeds of two million miles per hour and made a giant bubbles north and south of the black holes that extend for tens of thousands of light years. That kind of puts your uncle's last burp into perspective!

Wednesday, February 22, 2017

A Star With SEVEN Earth-like Planets

An international team of astronomers today announced that they have found a faint cool star that is surrounded by a system of seven planets, each of which resemble the Earth in size. Three of the planets orbits in what we call the "habitable zone" where water can be liquid and temperatures might be right for life.
The star, located about 40 light years away, is so faint and cool, it doesn't have a name like bright stars do. It's referred to by the name of the telescope that discovered it and given a number (TRAPPIST 1). Each of the planets is then given a letter from b to h. (See the diagram above.)
Note that the planets are all very close to their dim star, taking from 1.5 days to about 20 days to orbit it. (By comparison, the closest planet to the Sun, Mercury, takes 88 days to orbit.) Planets e, f, and g are the ones where the combination of a cool little star and close-by planet work out to make the temperatures potentially reasonable for life. This star enters the record books as the one with the largest number of Earth-like planets, and the largest number of candidate planets in the habitable zone.
Astronomers caution that the kind of star these planets live around (called an "ultra-cool red dwarf") tends to have a lot of "activity" on its surface when they are young. Great flares of energy and particles are given off in this kind of activity, which might flood the nearby planets with high-energy radiation. That might not be so healthy for the formation of life there until the star settles down to a more stable adult existence.
On the other hand, such low-mass stars (this one contains only 8% of the "stuff" our Sun has) tend to live much much longer than a star like the Sun, so there may eventually be a much longer opportunity for the planets to evolve their surfaces and atmospheres and give birth to life.
Another complication for planets so very close to their star is that their motion probably resembles that of our Moon in a crucial way. The Moon (and these planets) take the same time to orbit as to spin, which means they keep the same face toward the object they go around. So one side of each planet always faces their star and the other side is always in darkness. There is no day and night cycle on these worlds -- you either live on the star-facing side and have perpetual day or you live on the other side and have perpetual night. Only a significant atmosphere might make such a world more bearable and astronomers are using a variety of telescopes to probe whether these planets are surrounded by an air layer and how much and what kind of air they have.
Just to put the discovery in context, astronomers now know over 3,000 planets orbiting other stars, ranging from balls of gas and liquid much bigger than Jupiter, down to rocky balls smaller than Venus. Experts now estimate that perhaps half of the stars in our Milky Way Galaxy may possess planets, and many stars will have more than one planet, just like TRAPPIST 1 and the Sun do. The universe seems rich with planets of all kinds, making it more likely than ever that we are not the only form of semi-intelligent life in the cosmos.

Below is a little poster NASA created to show how the other planets in this system would look from the surface of one of them.

Sunday, February 12, 2017

Why Should I Believe a Word of This?

        In June of 2016, the students at my college asked me to be the Commencement Speaker. I was honored and touched, and talked about skeptical thinking and living a fact-based life. The newsletter "Skeptical Briefs" has just published a one-page version of my talk and I've put it up on the web, in case anyone might like to read it: 

Wednesday, January 18, 2017

A New Photo of the Death-Star Moon

Just in time to anticipate the success of the Star Wars film "Rogue One", NASA released a new photo of Mimas, the moon of Saturn's that resembles the "Death Star."
Mimas, an icy world about 250 miles in diameter, has a giant crater on it which is 86 miles across. That's a single impact feature that is one third the diameter of the world that it’s on!!  Astronomers speculate that if the chunk that hit Mimas, exploded, and dug out that crater had been a little bit bigger it might well have shattered that moon.  Then Saturn might have had another ring system around it.
The crater has been named “Herschel” after the astronomer (and musician) who discovered Mimas.  In its center is a mountain that towers almost as high as Mount Everest on Earth.  It’s that central peak that helps our mind’s eye see Mimas’ resemblance to the evil superweapon in the Star Wars series.
The photo was taken in October by the Cassini mission, which has been exploring Saturn, its rings, and its moons since July 2004.  Its spectacular images find their way into every course I teach and every tourist tour of the solar system I guide in my public lectures.

Sunday, January 8, 2017

A Photo of the Earth and Moon from Mars!

   NASA has just released a remarkable image of the Earth and the Moon as seen from a spacecraft orbiting Mars. Our planet and Mars were 127 million miles apart when the photo was taken.
   The Mars Reconnaissance Orbiter (MRO) has been orbiting Mars since 2006, collecting very detailed close-up images and data about the surface of the red planet. In this case it was used to capture a photo of Earth and Moon with both bodies in the same frame. The image was taken at a time when the Moon was behind Earth as seen from Mars, so it shows the Earth-facing side of our natural satellite.
   Even at Mars' distance, the image of the Earth reveals continents. Australia is the reddish-brown feature in the center. Seeing ourselves as a tiny disk of light in the blackness of space can help remind us that we share a fragile and beautiful planet in our journey through space.