NASA's Hubble Will Use Rare Stellar Alignment to Hunt for Planets

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June 3, 2013

J.D. Harrington 
Headquarters, Washington 
202-358-5241 
j.d.harrington@xxxxxxxx 

Ray Villard 
Space Telescope Science Institute, Baltimore, Md. 
410-338-4514 
villard@xxxxxxxxx 

RELEASE: 13-163

NASA'S HUBBLE WILL USE RARE STELLAR ALIGNMENT TO HUNT FOR PLANETS

WASHINGTON -- NASA's Hubble Space Telescope will have two 
opportunities in the next few years to hunt for Earth-sized planets 
around the red dwarf Proxima Centauri. 

The opportunities will occur in October 2014 and February 2016 when 
Proxima Centauri, the star nearest to our sun, passes in front of two 
other stars. Astronomers plotted Proxima Centauri's precise path in 
the heavens and predicted the two close encounters using data from 
Hubble. 

"Proxima Centauri's trajectory offers a most interesting opportunity 
because of its extremely close passage to the two stars," said 
Kailash Sahu, an astronomer with the Space Science Telescope 
Institute in Baltimore, Md. Sahu leads a team of scientists whose 
work he presented Monday at the 222nd meeting of American 
Astronomical Society in Indianapolis. 

Red dwarfs are the most common class of stars in our Milky Way galaxy. 
Any such star ever born is still shining today. There are about 10 
red dwarfs for every star like our sun. Red dwarfs are less massive 
than other stars. Because lower-mass stars tend to have smaller 
planets, red dwarfs are ideal places to go hunting for Earth-sized 
planets. 

Previous attempts to detect planets around Proxima Centauri have not 
been successful. But astronomers believe they may be able to detect 
smaller terrestrial planets, if they exist, by looking for 
microlensing effects during the two rare stellar alignments. 

Microlensing occurs when a foreground star passes close to our line of 
sight to a more distant background star. These images of the 
background star may be distorted, brightened and multiplied depending 
on the alignment between the foreground lens and the background 
source. 

These microlensing events, ranging from a few hours to a few days in 
duration, will enable astronomers to measure precisely the mass of 
this isolated red dwarf. Getting a precise determination of mass is 
critical to understanding a star's temperature, diameter, intrinsic 
brightness, and longevity. 

Astronomers will measure the mass by examining images of each of the 
background stars to see how far the stars are offset from their real 
positions in the sky. The offsets are the result of Proxima 
Centauri's gravitational field warping space. The degree of offset 
can be used to measure Proxima Centauri's mass. The greater the 
offset, the greater the mass of Proxima Centauri. If the red dwarf 
has any planets, their gravitational fields will produce a second 
small position shift. 

Because Proxima Centauri is so close to Earth, the area of sky warped 
by its gravitation field is larger than for more distant stars. This 
makes it easier to look for shifts in apparent stellar position 
caused by this effect. However, the position shifts will be too small 
to be perceived by any but the most sensitive telescopes in space and 
on the ground. The European Space Agency's Gaia space telescope and 
the European Southern Observatory's Very Large Telescope on Mt. Cerro 
Paranal in Chile may be able to make measurements comparable to 
Hubble's. 

To identify possible alignment events, Sahu's team searched a catalog 
of 5,000 stars with a high rate of angular motion across the sky and 
singled out Proxima Centauri. It crosses a section of sky with the 
apparent width of the full moon as observed from Earth every 600 
years. 
For more information about NASA's Hubble Space Telescope, visit: 

http://www.nasa.gov/hubble 

	
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