New Exoplanet Clue to Future of The Solar System

Telling the future can be difficult - look at how difficult it can be to predict the weather. But in new research published in Nature, led by Australian Joshua Blackman from the University of Tasmania, astronomers have discovered an exoplanet that may give hints as to what our Solar system will look like in the future. The Jupiter-mass planet is orbiting a white dwarf star, and its presence may indicate what will happen in our system when the Sun reaches the end stages of its life in several billion years from now. 

This latest exoplanet discovery suggests that Jupiter could survive the ordeal of the Sun becoming a white dwarf. The system consists of a white dwarf roughly half the mass of our sun orbited by the planet MOA2010BLG477Lb. The planet has a mass equivalent to 1.4 times that of Jupiter, orbiting roughly 2.8 AU away from its host star.  

Models have previously implied that this type of system is theoretically possible, however, the new exoplanet, MOA2010BLG477Lb, is the first observed instance of a planet of Jupiter-mass surviving their host star transitioning from main-sequence to red giant, to white dwarf.  

Far into the future, the Sun (as a main sequence star) will burn through and exhaust its hydrogen fuel source that it fuses to generate energy in its core. At this point, the Sun will then expand into a red giant - engulfing the inner planets, before puffing away its outer layers, leaving only a hot cinder core known as a white dwarf. 

These objects are highly dense and contain up to 1.4 times the mass of the Sun in a small, planet-sized radius. They are the result of the phase of evolution of progenitor main sequence stars (usually to about eight solar masses) once they have exhausted burning through several nucleosynthesis phases, where many of the elements we see around us are created. 

When this expansion happens, however, the Sun will become so large that during this process it will not only destroy some of the planets in our Solar system, it will also destablise their orbits, and push out the habitable zone from where the Earth is located, out to greater distances. But some questions that researchers have been considering remain, like would any of the planets survive this process, and what would the new system look like once the white dwarf is in place? 

The new exoplanet was first detected in 2010 via microlensing. Microlensing works by observing the bending of a background light (such as a white dwarf) by a foreground massive object (such as a planet). In this way, even white dwarfs and their orbiting planets can be detected.  

Microlensing is a technique that is also sensitive to cold planets (those which orbit far from their stars) down to the mass of Earth. Typically astronomers may rely on light-detection-based techniques, such as exoplanet transits to find exoplanets, but these methods aren’t sufficient to see planets that are orbiting white dwarfs - a type of star which emits relatively little light and is roughly the size of Earth. 

In this latest research, the system was examined by obtaining near-infrared deep exposures of the field surrounding the planet using the Keck II telescope located on Mauna Kea, Hawaii. Comparing this data with other local white dwarfs, and by determining how far away the planet is from its host, they determined that the planet and star formed at the same time, meaning that the planet had survived the star’s transformation into a white dwarf. 

Based on these findings, the researchers extrapolate that when our Sun goes through the process of becoming a white dwarf, it will likely engulf Mercury and Venus, but Jupiter will survive the ordeal. 

Video Credit: W. M. Keck Observatory/Adam Makarenko.