Any unexpected kink in the debris disk surrounding a young star is often attributed to a planet forming amongst the gas and dust. But that may not be the only explanation. In fact, new work by John Debes and team at NASA GSFC points to an alternative: The motion of the infant system through insterstellar gas. Thus we have yet another reminder that space is not truly empty, and that patches of gas can play their role in planet formation. Debes and colleagues have been looking at infant systems like that around the star HD 32297, some 340 light years from Earth in the constellation Orion. About 100 million years old, the star is surrounded by a dust disk that resembles what our Solar System probably looked like not long after the major planets formed. Noticing that the dust disk around the star was warped, the team was led to link the finding to the presence of nearby interstellar gas clouds. The idea of interstellar gas drag upon a stellar system moving through such a cloud seems a...

We often speak about planets migrating from the outer to the inner system of a star, something that helps us put 'hot Jupiters' in context. But what about migration within the galactic disk? It's an idea under continuing investigation. In the absence of direct observational evidence, we infer migration and assume that older stars often come from regions with significantly different metallicity than stars in their current environment. The presumed origin would be the inner disk, which Misha Haywood defines as that part of the galaxy inside the radius from galactic center to our Sun. Dave Moore sent me Haywood's latest paper a few months back and I've been slow in getting to it because I wanted to give its conclusions further thought. It's intriguing stuff. Haywood (Observatoire de Paris) takes note of the fact that we tend to find gas giants around stars that are rich in metals (here a pause to remind newcomers that by 'metals,' we mean elements higher than helium). And he wants to...

?by Larry Klaes Tau Zero journalist Larry Klaes here gives us a quick overview of the history and future of the Earth, so vital for understanding not only how life emerged here but how it may appear around other stars. It's good to keep this background in mind as Kepler and COROT go planet-hunting. Thus far we've had our share of surprises as we've explored other systems, and doubtless there will be many more as future instruments come online, both in space and on the ground. And as Larry reminds us, there is much we still have to learn about our own planet. Let's look at our celestial home’s place in time as well as space, namely the long and ancient history of its cosmic birth and development. This story includes a general history of the wide variety of living beings that dwell just about everywhere on this planet. Planet Formation and the Big Collision Earth’s geological history began about five billion years ago, roughly eight billion years after the Universe got its start in the...

A conference like the recent on in Aosta offers plenty of opportunity to listen in on fascinating conversations, one of which had to do with what would happen if we found a brown dwarf closer to the Earth than the Centauri stars. The general consensus was that such a find would be a powerful stimulus to the public imagination and would probably result in renewed interest in getting to and exploring such a place. A boon, in short, for all our interstellar efforts, an awakening to a new set of possibilities. But if there were a brown dwarf that close, wouldn't we have other signs of it? One figure I heard mentioned at Aosta was three light years. Here I have to do some checking, because I don't recall who dropped that figure or what paper he was referring to, but the upshot was that someone has argued that even a small brown dwarf closer to the Sun than three light years would leave an unmistakable signature in the orbits of our Solar System's planets. I'll see if I can track down the...

Why some planets are the size they are remains something of a mystery. I'm looking at the discovery paper for a planet called WASP-17b, which is said to be twice Jupiter's size but only half its mass. That raises questions about the mechanisms at work, for you can't explain the bloated nature of this world with the models of planetary evolution we're now working with without factoring in massive tidal effects. In one sense, WASP-17b is completely anomalous. In addition to its size, it orbits its star in retrograde fashion, opposite the direction of the star's spin. But in other important respects, the new planet joins the ranks of other bloated worlds like HD209458b (the first such world to be discovered), and a flock of other huge planets that includes TrES-4, WASP-12b, XO-3b and HAT-P-1b. TrES-4 shows a density about fifteen percent that of Jupiter, with a radius 1.78 times larger than Jupiter's. Image: Orbiting close to its parent star, WASP-17b may look something like this, a...

It doesn't take much observation to realize that the early Solar System was a violent place. Mercury seems stripped of its outer crust, doubtless the result of a massive impact, while Uranus was knocked to one side at some point in its history, aligning its spin axis with the plane of the ecliptic. Venus was hit so violently that it rotates clockwise as seen from above, opposite to the other planets. At least, a collision is one of several theories that may explain Venus' retrograde rotation, and it's more than plausible. 100 light years from Earth is a place that reminds us of the impact that produced Earth's own moon billions of years ago. HD 172555 is a young star in the southern constellation Pavo (the Peacock), its twelve-million year old system in its infancy. Spectral analysis from the Spitzer Space Telescope shows clear evidence of a collision much like that between the Earth and that early, Mars-sized object that once struck it. Image: This artist's concept shows a celestial...

Unlike the Cassini Saturn orbiter, which we looked at yesterday in the context of cryovolcanism on Titan, the Kepler spacecraft has but a single scientific instrument. It's a photometer based on a Schmidt telescope design with a 95 cm aperture and a field of view larger than 100 square degrees. Measuring brightness variations for over 100,000 stars, Kepler is the first mission that should be able to detect Earth-size planets in the habitable zones of their stars. That made yesterday's news conference an eagerly anticipated event, but we have to remember that it's going to be a while before we start talking about terrestrial planet detections. It takes multiple transits and much data analysis to make that possible, and a transiting world at roughly Earth-like distance from its star will demand several years of work. Kepler's baseline mission is three and a half years, more than enough to make such detections, and the good news is that the instrument works. Image: Magnified Kepler...