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Is our solar system missing a planet?

Possibly, according to some scientists who are trying to understand the early days of Sol and friends.

One way that researchers study events like the creation of the solar system is to model what might have happened using computer software. The basic idea works like this: We know a decent amount about the physical laws (like gravity) that govern the creation of planets and the formation of a solar system. So scientists can take those laws, and program them into a virtual universe that also includes other real-world data ... like what we know about the make-up of the Sun and the planets orbiting it. Then, they recreate history. Then they do it again. Over and over and over, thousands of times, the scientists witness the creation of our solar system.

It doesn't happen the same way each time. Just like you can get a very different loaf of bread out of multiple attempts and baking the same general recipe. But those recreations start to give us an idea of which scenarios were more likely to have happened, and why. If our solar system tends to form in one way and resist forming in another, we have a stronger basis for assuming that the former way was more likely to be what really happened.

That's what you're seeing in this study, which Charles Q. Choi writes about for Scientific American.

Computer models showing how our solar system formed suggested the planets once gravitationally slung one another across space, only settling into their current orbits over the course of billions of years. During more than 6,000 simulations of this planetary scattering phase, planetary scientist David Nesvorny at the Southwest Research Institute in Boulder, Colo., found that a solar system that began with four giant planets [as ours currently has] only had a 2.5 percent chance of leading to the orbits presently seen now. These systems would be too violent in their youth to end up resembling ours, most likely resulting in systems that have less than four giants over time, Nesvorny found.

Instead, a model about 10 times more likely at matching our current solar system began with five giants, including a now lost world comparable in mass to Uranus and Neptune. This extra planet may have been an "ice giant" rich in icy matter just like Uranus and Neptune, Nesvorny explained.

Read the rest

Is Voyager I outside our solar system?

Probably not yet. But it's on the cusp. And part of what makes this entire process really, really interesting is that, by the very nature of this whole experiment, we don't know exactly what will happen when Voyager I does cross that imaginary boundary line. But, as Rebecca Rosen explains on The Atlantic, we do have some pretty good theories.

Some cosmic ray particles enter the heliosphere and we can see them here from Earth. But a slower type has a hard time entering the heliosphere. Last month, the sum of those slower particles, suddenly ticked up about 10 percent, "the fastest increase we've seen," Stone says. But an uptick does not mean Voyager has crossed over, though it does mean we're getting close. When Voyager does finally leave and enter the space "out there where all the particles are," the level will stop rising. The rising itself means that Voyager is not out there, yet. "But," cautions Stone, "we don't know. I mean this is the first time any spacecraft has been there." Since nothing's ever been there before, we don't know what it will look like, which makes it a little hard to recognize "it" at all. "That's the exciting thing," he continues.

This is the most exciting kind of science—the sort where we really don't know the answers and we're on the cusp of learning something truly, wonderously new. Stay tuned.

Read Rebecca Rosen's full article at The Atlantic

The practical side of the transit of Venus

The transit of Venus is cool.

I think we can all agree on that. On Tuesday, the planet Venus will pass between us and the Sun—a little black dot sliding across the face of a giant, yellow ball. Barring the Singularity, this will be your last opportunity to see a transit of Venus. The next one won't happen until December of 2117.

But, beyond looking nifty and reminding you of your own mortality, what, exactly, is the transit of Venus good for? Is this a cultural event, a scientific event, or a little of both?

Historically, the transit of Venus provided the data that allowed us to gauge the size of the solar system for the first time. This time around, according to Space.com, researchers will be watching the transit with an eye to the universe outside our solar system. That's because what we learn from the transit of Venus could help us identify planets (including Earth-ish planets) elsewhere in the galaxy.

Astronomers already key in on transits to search for alien worlds, often finding them by detecting the telltale dips in brightness exoplanets cause when they pass in front of their parent stars. NASA's Kepler space telescope has been very successful using this technique, flagging more than 2,300 candidate alien planets to date.

“During the transit, Venus Express will make important observations of Venus’ atmosphere that will be compared with ground-based telescopes to help exoplanet hunters test their techniques," said Håkan Svedhem, ESA’s Venus Express project scientist.

Read the rest of the Space.com story

Find lots of educational materials, how-tos, and useful transit of Venus information at TransitofVenus.org

Check out Discovery News' guide to safely photographing the transit of Venus

The beautiful surface of the Sun

Phil Plait linked to this amazing photo of the Sun on the Bad Astronomy blog today. It's incredible. Like nothing I've ever seen before. The photographer is Alan Friedman. Plait explains how Friedman got this look, which is a very nice reminder that space photography is seldom really about "point and click".

Alan uses an Hα filter, which cuts out almost all the light from the Sun except for a narrow slice of color emitted by warm hydrogen. This reduces the glare hugely, and reveals delicate structures in the Sun’s plasma. He then inverts the image, so bright things appear dark, and vice-versa. That’s an old astronomer’s trick that makes fainter things easier to see.

Like this close-up? Go to the Bad Astronomy blog to see Alan Friedman's photo of the full Sun. Your mind will be blown. I promise.

What happens at the edge of the solar system?

This is a drawing of what the edge of the solar system might look like, as envisioned by plasma physicist Merav Opher. One of the few women in this field, Opher is also one of the top scientists, of any gender, studying what happens at the edges of space. John Rennie has written a great profile of Opher and her work. You really should read it. I like Rennie's work a lot. He's one of those amazing writers who can make abstract, theoretical physics feel as immediate, intense, and important as it actually is. To wit:

“The edge of the solar system” is more than a turn of phrase. A tenuous, invisible wind of ionized gas billows off the sun at a million miles per hour, carrying with it the sun’s magnetic field. It does not radiate out infinitely: far beyond Pluto’s orbit, this solar wind abruptly slams into the thin interstellar medium and the scattered gaseous remnants of exploded stars. That border defines what astronomers call the heliosphere.

Just a few years ago, Opher played a key role in explaining why the heliosphere is unexpectedly lopsided and off-kilter. Now an assistant professor in Boston University’s astronomy department, Opher is interpeting data that suggests that part of the heliosphere’s edge may be a churning magnetic froth, which could have broad implications for astrophysics.

Read the full profile at Txchnologist

Is the sun hard, or squishy? Reddit knows.

The collective genius of Reddit tackles a great science question from a toddler: Is the Sun hard or squishy? (Via Arria Belli)