Discovery Space: Next Generation

Strike a Pose, Gravity

What's the deal with gravity?

We don't know what causes it, but we do know it's a force that occurs when two objects -- such as the Earth and the moon -- attract to one another. We also know that if each object is treated as a perfect sphere, the math describing gravity is fairly simple.

But reality bites, and the Earth is not a perfect sphere. It has deep oceans and towering mountain peaks, and is thicker around the equator. Each little rock, pebble, grain of sand and molecule of water pulls on the moon, planets, the sun and everything else in the universe. Needless to say, accounting for these disturbances is a difficult problem.

Since before the first satellite launch, humanity has studied gravity anomalies, and those investigations have brought us to the Gravity Recovery and Climatology Experiment, aka "GRACE," which uses special satellites to measure this mysterious force.

See right for a 3-D map of these anomalies that the GRACE mission has teased out. The red indicates anomalies stronger than Earth's average pull of gravity (about 32.1740486 ft/s²), while the blue shows weaker-than-average anomalies.

Looks cool, but what do we do with this kind of information?

From modeling satellite orbits to monitoring the melting of glaciers and the polar ice caps, the benefits are numerous. To elaborate on the glacier example: If one is melting, the water drains away. That change in water means a change in mass -- and that translates to a small change in gravity around the glacier. So we can use gravity to study climate change.

Here's where I fit in: Scientists and engineers have used one type of gravity model for the past 100 years -- it's called spherical harmonics and is a bit dense to describe here (just look at the equation). My research looks at gravity from a totally different perspective, and to understand it, let's talk photography.

A photograph helps us preserve a memory, e.g. you as a kid. Years later, the picture reminds us of what we looked like when we were younger. That retrospective approach is similar to the gravity modeling I'm studying: Let's take our knowledge of the Earth's gravity, and store that information like a photograph so we can use it later. And instead of taking a picture of what the Earth visually looks like, we take a snapshot of what the Earth gravitationally looks like.

But one photograph doesn't show us the whole picture. If we take a picture of one side of the Earth, what does the other side look like? How do we know what gravity is like there? Even two pictures don't lend us a clear picture of the edges. We actually need six photographs to give us the Earth as a cube (see right).

So, why this new way versus the "old" way?

We've all sat there, waiting for a computer game or some piece of software to run... the more complex it is, the longer it takes for the computer to crunch the numbers. The "cubed sphere" model of gravity actually makes the software scientists use run faster -- so you get the speed of a rough test with the accuracy of an incredibly complex one. For people trying to model how their shiny new satellites will react to the Earth's anomalies while in orbit, that's a valuable improvement.

Modeling gravity is especially important for missions to the moon, since the spacecraft will be carrying people, and the moon's gravity is much more irregular than the Earth's. Better mapping of the moon's gravity not only improves simulations for planning trips there, but also helps astronauts figure out precisely where their spaceship is without asking for help from Earth.

It's also useful because, quite simply, someone can easily zoom in on a region they're interested in. Like looking at pictures of ourselves from when we were younger, we can use this cube-like model to easily see changes over time in things such as melting glaciers, mountains and more.

Brandon Jones is PhD student in aerospace engineering at the University of Colorado, Boulder.

Photos, top to bottom: Brandon Jones; NASA. Wikimedia Commons; Brandon Jones

Carnival of Space #67: Planets, Rockets, Books and Olympic Torches

Welcome to episode 67 of the Carnival of Space! I'm delighted to have a chance to host this roundup of interesting new blog posts on space and astronomy for the first time, and there's a lot to write about.

This blog, if you haven't visited before, is focused on the work of college students who are involved in astronomy and/or space exploration. The collection of postings described here don't relate directly to students, but they should be of interest to anybody, students included, who is fascinated by the stars and planets and by humanity's efforts to move out toward them. Welcome aboard!

For starters, there are a lot of interesting posts this week on the past, present and future of the human space program.

There's a fascinating bit of space history on David Portree's Altair VI blog, recalling the thoughts of a top space engineer during the heady days of the Apollo program in the 1960s. It casts an interesting light on what could have, should have happened after the first moon landings, and the squandered opportunities that could have been carried forward with minimal extra investment.

Bringing us up the present and near future, Political Action for Space takes a look at Congressional candidate Pete Olson's views about the space program's future and the retirement of the space shuttle, and encourages everyone to grill their own local representatives on their views.  Next Big Future looks at one of the specific issues that needs to be faced as we move toward having people go farther and spend more time in space: how to deal with radiation problems. And 21st Century Waves looks at the future of our space program and lunar exploration plans in terms of the economic impact of exploration, and has some interesting thoughts on Mike Griffin and NASA's plans.

Moving from the big picture to a close look at details of space travel, astrophysicist Ethan Siegel takes a close look at how liquids behave in space, complete with some intetresting video clips, on Starts With a Bang.

There's also a lot of postings this week on the latest in planetary news. Cassini recently made an amazingly close pass of Saturn's moon Enceladus and returned some lovely and enigmatic images. There's a nice description of the technical challenge of such a close flyby on Catholic Sensibility, and a collection of some of the puzzling pictures on Meridiani Journal. And Emily Lakdawalla does her usual thorough job of analyzing the pictures one by one on her Planetary Society Weblog, always a must-see blog for all news planetary.

Meanwhile, the summer's glut of new findings from Mars continues. In Cumbrian Sky, Stuart Atkinson has some nice reflections on Phoenix's exploration there, and how it's going in a different direction that the Mars rovers but nevertheless exciting. Dave Mosher talks about the new perchlorate discovery in his Space Disco. And then there's the discovery of clay minerals, which raises questions about the possibility of past life there, mentioned in a post on Meridiani Journal.

Some thoughts on a different way of looking at the debate over the definition of a planet, focusing on the time parameter instead of on current status, is on the Lounge of the Lab Lemming. And a nice recap of the history of the century-ago impact over Tunguska, Siberia is on A Mars Odyssey.

Moving farther out into the cosmos, a couple of posts this week look at a newly-discovered celestial oddity called Hanny's Voorwerp. A Babe in the Universe describes how the strange galactic object was discovered by a schoolteacher as part of a massive online search of new sky images. And Centauri Dreams takes this odd object as a starting point for looking at some of the possible implications for the Search for Extraterrestrial Intelligence. And Chris Lintott's Universe looks at the way this strange discovery has been covered in the popular press.

For those who would rather actually look at the sky than sit and ponder about it, some offerings include a guidebook to the constellation Saggitarius and its many denizens, on Visual Astronomy. And moving in from the gigantic to the infinitesimal, Ian O'Neill muses on the Higgs Boson and what is going to be found at the new Large Hadron Collider in his AstroEngine blog.

There's some really fun summer reading, for kids on up to adults, in  Out of the Cradle, which has a wonderful roundup of books about women and girls involved in space travel and astronomy. It's a great collection to inspire girls to realize that space really is not just an interest for boys, and for women who've already figured that out and just want some fun reading material.

I suppose you thought that this week's wall-to-wall news coverage of the Beijing Olympics is one area that really has nothing to do with our topics of space and astronomy, right? Wrong! Two different posts this week make the connection. CollectSpace has a description of the whole bunch of astronauts, cosmonauts and taikonauts who took part in the Olympic torch relay. And Kentucky Space's Jeff Manber reflects at length on the commentary about the Chinese space program in the Olympic coverage, and other thoughts about that whole program. Who knew?

Finally, some interesting philosophical musings on humanity's destiny and the meaning of life, and how our ambitions in exploring the planets fit into these larger themes, triggered by the reading of a couple of science fiction novels, in this post on Music of the Spheres.

(Photos: Top, Apollo 11 image from the moon; Middle, Enceladus image, courtesy of NASA; Bottom, Hanny's Voorwerp, from the Sloan Digital Sky Survey.)

The Solar System's Greatest Hits

The biggest wallop ever suffered by any planet during the violent, turbulent early days of the solar system was when something as big as Mars slammed into the Earth with such force that the entire crust melted and splattered off into space. Some of it fell back, and much of the rest globbed together and became the moon. That's something scientists only managed to figure out after analyzing the rocks brought back from the moon by the Apollo astronauts.

The second biggest hit, it seems, was one suffered by Mars, when it got clobbered by something bigger than Pluto. That idea, which has been kicking around since the mid-80s, was not taken very seriously until this week, but now suddenly gets catapulted into being the likeliest explanation for the strange lopsided surface of the red planet.

The new evidence for a colossal impact that left a deep gouge on Mars that's bigger than Eurasia  came out in a trio of papers published this week in the journal Nature. One of the papers used recent spacecraft data to reconstruct the outline of the giant basin on Mars -- the largest impact remnant ever seen anywhere. The other two papers used computer modelling to figure out exactly how big the impacting body must have been, and how fast and at what angle it struck Mars.

These are major, significant papers that apparently solve one of the biggest remaining mysteries about our planetary system, the riddle of why Mars has two such radically different hemispheres. These papers, though they will undoubtedly be debated for a few years as is the norm for any significant shift in scientific understanding, will likely stand as among the most important advances in planetary astronomy in recent decades. (See these stories in the New York Times, Christian Science Monitor, Discovery Channel  and National Geographic, for example)

One of those papers, an analysis of the size and direction of arrival of the impacting body, was done by a group at Caltech. And the lead author of the paper, Margarita Marinova, is a graduate student there. Kudos to Marinova for an important and groundbreaking piece of research.

Marinova, a graduate student in Caltech's Division of Geological and Planetary Sciences, found that the impactor must have been between 1,600 and 2,700 km. across, producing a 100 billion gigaton blast. "This size range of impacts only occurred early in solar system history," Marinova says. It all happened about 4 billion years ago, around the same time as the moon-forming crash. Those early days of the solar system were very violent times, when the planetesimals from which the planets were built were still in flux and there was a whole lot of crashing going on.

Sometimes student work in science is thought of, especially by outsiders, as sort of practice work, a kind of second-class level of research. But most scientists know very well that this example, of truly significant new findings, is actually pretty typical. Much of the cutting-edge work in science, in fact, is the product of student research projects.

It's nice to be reminded of that from time to time, as in this case.

By the way, in that same issue of Nature there's a whole package of articles related to impacts on Earth, timed to the fact that this Monday, the 30th, will be the 100th anniversary of the biggest terrestrial impact known to have been witnessed by people -- the Tunguska blast over Siberia in 1908. Among that collection of articles is one that I wrote -- a sort of oral history of how our understanding of near-Earth asteroids and the danger they pose has evolved over the last few decades. It's accompanied by a very clever cartoon, depicting some of the pioneers in that field (who were the subjects of my interviews). I take no credit for the illustration -- the idea came from my friend and Nature's news and features editor, Oliver Morton, and was quite brilliantly executed by the artist David Parkins.

The Ice Planet Mars

No, it's not a surprise, though some of the news reports have made it seem that way. We've actually known for decades that Mars has huge deposits of regular, plain old water ice -- a very exciting thing, since water is the staff of life as we know it. And unlike other ice-covered or ice-filled bodies, like comets, or the moons of Jupiter and Saturn, which are always very, very, very cold, on Mars the temperatures do sometimes climb above the freezing point. So liquid water is possible there, at least a bit below the surface in certain places -- and, though this is controversial, possibly even on the surface sometimes.

The air on Mars is so thin that it's practically a vacuum, though, so any exposed water, or even any exposed ice, turns to vapor very quickly. But pictures from as far back as the Viking mission in the 1970s even showed occasional frost on the ground in the early morning, just after sunrise. The presence of ice near the surface, and some water vapor in the atmosphere, is why Mars is such an exciting place for astrobiologists -- or for anybody who is interested in the possibility of life elsewhere. Especially since we know that in the very early days of Mars, around 4 billion years ago, water actually flowed across the surface and may have formed lakes or even an ocean. That's what makes Mars the most Earth-like place we know of besides, you know, Earth.

So, as I was saying, the fact that the new Phoenix lander on Mars has proved the existence of ice just beneath the surface, which was announced at a press conference yesterday, is not really a surprise. That's what Phoenix was mostly designed for, in fact -- to study the ice, by melting bits of it in tiny ovens, to see what chemicals it contains, and whether the kinds of molecules needed by living creatures are present there.

So, what was just announced -- little bits of ice just below the surface, which were revealed by Phoenix's trench-digging tool, and which had vaporized within a few days -- is not at all surprising, but it is very important. It means that the hoped for ice is present at the place where Phoenix touched down, close to the northern polar region of Mars, and that it's very close to the surface and easy to reach.

That's pretty much what Phoenix chief scientist Peter Smith of the University of Arizona and the rest of the science team had hoped, and even expected. But hoping and expecting is a very different thing from actually proving it on the ground.

So this means there's every chance that, despite some mechanical and software glitches, the mission will be able to do what it set out to do, and could end up providing better evidence than ever before that Mars may be a habitable place.

But, contrary to other reports you may have read, one thing Phoenix will not do is prove whether there are any living organisms there now, or ever were in the past. That's because even though it has equipment to carry out the most detailed chemical tests ever done on Mars, as well as the highest-resolution microscopy, it does not have anything that could detect signs of life itself. And that's a darn shame.

The Viking mission, 32 years ago, was the only Mars mission that ever carried life-detection equipment, and it's results were controversial. The scientist in charge of one of the three life detection experiments on that mission is absolutely convinced that it did find life. Other members of the science team thought not. There's a very simple followup experiment that could prove it one way or the other, but in all these years, with four successful landers (and a few failures) on the planet since then, nobody has bothered to send that followup test.

What, the question of whether Earth is or isn't the only place in the universe with life isn't important enough to be worth checking?

Well, if Phoenix finds signs suggesting that the conditions for life are present, maybe that will spur NASA, or ESA, or JAXA, or somebody to go and look. Let's hope so.

The Phoenix mission, by the way, is the first mission ever sent to another planet whose control center, instead of being at a NASA center (or a Russian government space center) is actually on a college campus. It's located at the University of Arizona in Tucson. That's a wonderful new trend, and hopefully will offer some lucky students there a chance to watch, and maybe even participate in, a cutting edge planetary exploration mission. I'll be talking to them soon, and will report on how the presence of a Mars Mission Control on campus is affecting the students there.

(Photo credit: NASA/JPL-Caltech/University of Arizona/Texas A&M University)