Measure the beam from a pulsar for an hour or so and you’ll see all kinds of interference fringes in amongst the noise.  This intereference is caused by light scattered from the interstellar medium, probably in the form of whisps of  gas and dust although nobody knows for sure.

There’s all kinds of infromation locked in this data. In fact, this interference pattern can be thought of as a kind of  hologram of the interstellar medium. But to unlock it, to reconstrcut the image from the interference  data, you’ve gotta know the structure of the light field before it was distorted and this depends on thousands of unknown parameters.

A few astrophysicists have tried to reconstruct these holograms by guessing what these parameters should be but their results have been predictably poor.

Now Mark Walker at the University of Sydney and a few cobbers have made a dramatic improvement by developing an algorithm that can simultaneously optimise the eight thousand coefficients that describe the electric field.

This has allowed them to reconstruct the field and create an image of the interstellar medium. It’s impressive work.
Having done that, Walker and co say the information can be used to correct other observations of the  such as timing measurements on the pulsar beams. And it might also give an idea what’s doing all this scattering and how it changes over very short time scales.
Cool stuff.

Ref:  arxiv.org/abs/0801.4183: Interstellar Holography

Not alotta of planets around other stars could support life judging by the criteria we look for now: the possible presence of liquid water. In fact none of ’em could (with the possible exception of one).

But our method for determining whether liquid water could be present is crude to say the least. It’s based on the luminosity and distance of a planet from its sun which gives a rough idea of its average temperature. If that falls into the range of liquid water, then bingo.

So a new method of calculating habitability is needed says David Speigel and his mates at Columbia University in New York, (which is itself habitable only at certain times of the year).

This new method has gotta take into account all the new things we’ve been learning about life (that it can survive at temperatures ranging  from -85 degrees C to 130 degrees C), about climate models and radiative balance and about other planets themselves, most of which have much more eccentric orbits than ours and so have more extreme seasons.

It may be that on these planets only a small fraction of the surface can support liquid water and life. And if that’s the case, its signature would be too faint to spot.

It makes sense to limit our search to planets that not only have life. but enough of it to be detectable to us. Spiegel suggests that there may be some critical fraction of habitability below which we cannot detect life, even if it is there.  For example, only 85 per cent of the Earth’s surface is habitable, a number which varies from year to year.

All that means that astrobiologists have got some hard work ahead of em. It also means that a re-analysis of the one planet that might harbour liquid water, a planet about 5 times Earth’s size orbiting a red dward in the constellation of Libra, might produce some encouraging results.

Ref: arxiv.org/abs/0711.4856: Habitable Climates