Tag: breakthrough initiative

The Directly Imaged World Around α Centauri?

Optical and X-ray (cut-out) image of the Alpha Centauri binary stars (Optical: Zdenek Bardon; X-ray: NASA/CXC/Univ. of Colorado/T. Ayres et al.)

There is something terribly exciting about actually seeing an exoplanet. While we have discovered over 4,000 planets outside the solar system, the majority of these worlds have been identified through their influence on their star, either via a dimming of the star’s light as the planet transits across its surface, or the wobble of the star from the planet’s gravitational pull. These are incredibly powerful techniques for planet hunting, but neither allow us to actually lay eyes on the planet itself.

The method to actually see a planet is known as “direct imaging” and it is a tricky process, as the star’s light can easily overwhelm any radiation coming from the smaller, cooler planet. Exoplanet imagining has therefore focused on young Jupiter-sized worlds orbiting far from the powerful lighthouse of the star. These planets are large and their recent formation has left them packed with heat, with temperatures around 1340°F (727°C). Such hot houses emit thermal radiation at wavelengths around 5 microns, so most of the instruments dedicated to capturing planet pictures operate around this wavelength range.

Direct imaging of exoplanets is difficult, and so far has been mainly restricted to young, massive planets. This amazing animation of four planets more massive than Jupiter orbiting the young star HR 8799 includes images taken over seven years at the W.M. Keck observatory in Hawaii. (Jason Wang and Christian Marois)

However, these wavelengths are a bad choice if you want to try imaging an Earth-like world. As an evolved planet on a temperate orbit, thermal emission from a planet like our own is longer at about 10 – 20 microns. This is an awkward wavelength for observations from the Earth, as the Earth’s own thermal emission can swamp the distant signal of the planet.

Yet, being able to directly image temperate planets is an important technique for studying possible habitable worlds. As you move away from the star, the chances of the planet’s orbit transiting across the star’s surface from our view from Earth decreases. For a planet on a similar orbit to the Earth around a sun-like star, the probability is less than 0.5%. The only way to study many of these worlds may be if we can see them directly, and space-based observatories have been generally seen as the path to this kind of imaging.… Read more

Waiting on Enceladus

NASA's Cassini spacecraft completed its deepest-ever dive through the icy plume of Enceladus on Oct. 28, 2015. Credits: NASA/JPL-Caltech

NASA’s Cassini spacecraft completed its deepest-ever dive through the icy plume of Enceladus on Oct. 28, 2015. (NASA/JPL-Caltech)

Of all the possible life-beyond-Earth questions hanging fire, few are quite so intriguing as those surrounding the now famous plumes of the moon Enceladus:  what telltale molecules are in the constantly escaping jets of water vapor, and what dynamics inside the moon are pushing them out?

Seldom, if ever before, have scientists been given such an opportunity to investigate the insides of a potentially habitable celestial body from the outside.

The Cassini mission to Saturn made its closest to the surface (and last) plume fly-through a year ago, taking measurements that the team initially said they would report on within a few weeks.

That was later updated by NASA to include this guidance:  Given the important astrobiology implications of these observations, the scientists caution that it will be several months before they are ready to present their detailed findings.

The reference to “important astrobiology implications” certainly could cover some incremental advance, but it does seem to at least hint of something more.

I recently contacted the Jet Propulsion Lab for an update on the fly-through results and learned that a paper has been submitted to the journal Nature and that it will hopefully be accepted and made public in the not-too-distant future.

All this sounds most interesting but not because of any secret finding of life — as some might infer from that official language.  Cassini does not have the capacity to make such a detection, and there is no indication at this point that identifiable byproducts of life are present in the plumes.

What is intriguing is that the fly-through was only 30 miles above the moon’s surface — the closest pass through a plume ever by Cassini — and so presumably its instruments produced some new and significant findings.

The scientists writing the paper could not, of course, discuss their findings before publication.  But Jonathan Lunine, a Cornell University planetary scientist and physicist on the Cassini mission with a longtime and deep interest in Enceladus, was comfortable discussing what is known about the moon and what Cassini (and future missions) still have to explain.

And thanks to that briefing, it became apparent that whatever new findings are coming, they will not make or break the case for the moon as a habitable place. Rather, they will essentially add to a strong case that has already been made.… Read more

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