Using the Moon as a mirror — Hubble to watch transit of Venus in reflected light

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This mottled landscape showing the impact crater Tycho is among the most violent-looking places on our Moon. But astronomers didn’t aim the NASA/ESA Hubble Space Telescope in this direction to study Tycho itself. The image was taken in preparation for the transit of Venus across the Sun’s face on on 5-6 June 2012.

Hubble cannot look at the Sun directly, so astronomers are planning to point the telescope at Earth’s Moon and use it as a mirror to capture reflected sunlight. During the transit a small fraction of that light will have passed through Venus’s atmosphere and imprinted on that light astronomers expect to find the fingerprints of the planet’s atmospheric makeup.

These observations will mimic a technique that is already being used to sample the atmospheres of giant planets outside our Solar System passing in front of their stars. In the case of the Venus transit observations, astronomers already know the chemical makeup of Venus’s atmosphere, and that it shows no signs of life. But they can use the event to test whether their technique has a chance of detecting the very faint fingerprints of the atmosphere of an Earth-like planet around another star.

This image shows an area approximately 700 kilometres across, and reveals lunar features as small as roughly 170 metres across. The large bullseye near the top of the picture is the impact crater itself, caused by an asteroid strike about 100 million years ago. The bright trail radiating from the crater were formed by material ejected from the impact area during the asteroid collision. Tycho is about 80 kilometers wide and is circled by a rim of material rising almost 5 kilometers above the crater floor.

Because the astronomers only have one shot at observing the transit, they had to carefully plan how the study would be carried out. Part of their planning included these test observations of the Moon made on 11 January 2012.

This is the last time this century sky watchers can view Venus passing in front of the Sun, as the next transit will not happen until 2117.

The image was produced by Hubble’s Advanced Camera for Surveys. A narrow strip along the centre, and small parts of the upper left part of the image were not imaged by Hubble during its observations, and show data from lower-resolution observations made by a ground-based telescope.

Credit:

NASA, ESA, D. Ehrenreich (Institut de Planétologie et d’Astrophysique de Grenoble (IPAG)/CNRS/Université Joseph Fourier)

Source: spacetelescope.org

NASA | Evolution of the Moon (by NASAexplorer)

From year to year, the moon never seems to change. Craters and other formations appear to be permanent now, but the moon didn’t always look like this. Thanks to NASA’s Lunar Reconnaissance Orbiter, we now have a better look at some of the moon’s history. Learn more in this video!

This video is public domain and can be downloaded at:http://svs.gsfc.nasa.gov/goto?10930

Source: youtube.com

VLT Rediscovers Life on Earth

By looking at the Moon

29 February 2012

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By observing the Moon using ESO’s Very Large Telescope, astronomers have found evidence of life in the Universe — on Earth. Finding life on our home planet may sound like a trivial observation, but the novel approach of an international team may lead to future discoveries of life elsewhere in the Universe. The work is described in a paper to appear in the 1 March 2012 issue of the journal Nature.

“We used a trick called earthshine observation to look at the Earth as if it were an exoplanet,” says Michael Sterzik (ESO), lead author of the paper [1]. “The Sun shines on the Earth and this light is reflected back to the surface of the Moon. The lunar surface acts as a giant mirror and reflects the Earth’s light back to us — and this is what we have observed with the VLT.”

The astronomers analyse the faint earthshine light to look for indicators, such as certain combinations of gases in the Earth’s atmosphere [2], that are the telltale signs of organic life. This method establishes the Earth as a benchmark for the future search for life on planets beyond our Solar System.

The fingerprints of life, or biosignatures, are hard to find with conventional methods, but the team has pioneered a new approach that is more sensitive. Rather than just looking at how bright the reflected light is in different colours, they also look at the polarisation of the light [3], an approach called spectropolarimetry. By applying this technique to earthshine observed with the VLT, the biosignatures in the reflected light from Earth show up very strongly.

Co-author of the study Stefano Bagnulo (Armagh Observatory, Northern Ireland, United Kingdom) explains the advantages: “The light from a distant exoplanet is overwhelmed by the glare of the host star, so it’s very difficult to analyse — a bit like trying to study a grain of dust beside a powerful light bulb. But the light reflected by a planet is polarised, while the light from the host star is not. So polarimetric techniques help us to pick out the faint reflected light of an exoplanet from the dazzling starlight.”

The team studied both the colour and the degree of polarisation of light from the Earth after reflection from the Moon, as if the light was coming from an exoplanet. They managed to deduce that the Earth’s atmosphere is partly cloudy, that part of its surface is covered by oceans and — crucially — that there is vegetation present. They could even detect changes in the cloud cover and amount of vegetation at different times as different parts of the Earth reflected light towards the Moon.

“Finding life outside the Solar System depends on two things: whether this life exists in the first place, and having the technical capability to detect it,” adds co-author Enric Palle (Instituto de Astrofisica de Canarias, Tenerife, Spain). “This work is an important step towards reaching that capability.”

“Spectropolarimetry may ultimately tell us if simple plant life — based on photosynthetic processes — has emerged elsewhere in the Universe,” concludes Sterzik. “But we are certainly not looking for little green men or evidence of intelligent life.”

The next generation of telescopes, such as the E-ELT (the European Extremely Large Telescope), may well be able to bring us the extraordinary news that the Earth is not alone as a bearer of life in the vastness of space.

Notes

[1] Earthshine, sometimes called the old Moon in the new Moon’s arms, can easily be seen with the unaided eye and is spectacular in binoculars. It is best seen when the Moon is a thin crescent, about three days before or after new Moon. As well as the bright crescent the rest of the lunar disc is visible, dimly illuminated by the bright Earth in the lunar sky.

[2] In the Earth’s atmosphere, the main biologically produced gases are oxygen, ozone, methane and carbon dioxide. But these can all occur naturally in a planet’s atmosphere without the presence of life. What constitutes a biosignature is the simultaneous presence of these gases in quantities that are only compatible with the presence of life. If life were suddenly to disappear and no longer continuously replenish these gases they would react and recombine. Some would quickly disappear and the characteristic biosignatures would disappear with them.

[3] When light is polarised, its component electric and magnetic fields have a specific orientation. In unpolarised light the orientation of the fields is random and has no preferred direction. The trick used in some 3D cinemas involves polarised light: separate images made with differently polarised light are sent to our left and right eyes by polarising filters in the glasses. The team measured the polarisation using a special mode of the FORS2 instrument on the VLT.

More information

This research was presented in a paper, “Biosignatures as revealed by spectropolarimetry of Earthshine”, by M. Sterzik et al. to appear in the journal Nature on 1st March 2012.

The team is composed of Michael F. Sterzik (ESO, Chile), Stefano Bagnulo (Armagh Observatory, Northern Ireland, UK) and Enric Palle (Instituto de Astrofisica de Canarias, Tenerife, Spain).

The year 2012 marks the 50th anniversary of the founding of the European Southern Observatory (ESO). ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 40-metre-class European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Links

More information

Source: eso.org

GRAIL Mission Returns First Video of Moon’s Far Side (by JPLnews)

NASA’s GRAIL mission has beamed back its first video of the far side of the moon. The imagery was taken on Jan. 19 by the MoonKAM aboard the mission’s “Ebb” spacecraft.

Source: youtube.com

So what is GRAIL anyway?

I was sitting around, thinking… Like I sometimes do… And I got to thinking about GRAIL. There’s been a lot of news and excitement about it recently, but what does it actually do?

GRAIL is the Gravity Recovery and Interior Laboratory. It consists of two almost identical spacecraft, who’s mission is to measure the gravitational field of the Moon, so that scientists on Earth can use the data it collects to X-ray the Moon to reveal subsurface features and it’s thermal history.

Sounds good so far, right? But how does it actually measure the gravitational field? Well, the GRAIL spacecraft transmit radio signals between them, to gauge their distance from each other, as they orbit the moon in tandem. As they orbit, changes in the moons gravitational field will cause the distance between them to vary, allowing NASA scientists to create a map of the Moons interior and allow them to see what happens beneath the surface. It should also help them understand how Earth and other rocky planets in the solar system developed, and maybe we’ll find out if the Moon still has a molten core.

GRAIL’s primary mission is due to last 90 days. After this, a five-day decommissioning period is planned, and the spacecraft should impact the Moon’s surface 40 days later.

For more information visit NASA’s GRAIL mission page

-Pete

Image Credit: GRAIL Artist’s Rendition - NASA