Rare Stellar Alignment Offers Opportunity to Hunt for Planets

The nearest star to our Sun, the red dwarf Proxima Centauri, is on a course for a rare conjunction with two distant background stars. This alignment will offer astronomers a unique opportunity to look for planets orbiting close to Proxima Centauri. In addition, astronomers will be able to precisely measure the mass of this isolated red dwarf. 

NASA, ESA, K. Sahu and J. Anderson (STScI), H. Bond (STScI and Pennsylvania State University), M. Dominik (University of St. Andrews), and Digitized Sky Survey (STScI/AURA/UKSTU/AAO)

Observations from NASA’s Hubble Space Telescope in 2012 were used to plot the star’s trajectory across the sky with enough precision that astronomers can predict two “close encounters” of the stellar kind with Proxima Centauri. The red dwarf has passed nearly in front of a 20th-magnitude background star in October 2014 and it will pass a 19.5-magnitude star in February 2016.

The warping of space by Proxima Centauri’s gravitational field will cause the image of each star to be very slightly offset from their real positions on the sky. The amount of offset can be used to measure Proxima Centauri’s mass — the greater the offset, the greater the mass of Proxima. If Proxima Centauri has a planet, it may produce a small second position shift due to the companion planet’s gravitational field.

The stars will shift very slightly in their apparent position, an estimated 0.5 milliarcsecond and 1.5 milliarcseconds, respectively. (A milliarcsecond is the angular width of a nickel in Honolulu, Hawaii, as viewed from the distance of New York City.) Hubble can make measurements as small as 0.2 milliarcsecond.  These so-called microlensing events will last from a few hours to a few days.