Astronomers have recently discovered a tilted solar system, comprising of two planets that are orbiting their host star at an unusual angle to its equator. The observations were retrieved from NASA’s Kepler spacecraft, surprising an international team of scientists.
During a recent press statement, posted on the Iowa State University website, one of the institution’s professors of physics and astronomy, and a co-author of the research study, Steve Kawaler, discussed the importance of their efforts:
“This is a new level of detail about the architecture of a planetary system outside our solar system. These studies allow us to draw a detailed picture of a distant system that provides a new and critical test of our understanding of how these very alien solar systems are structured.”
Solar System Formation & Tilted Planets
In many parts of the Milky Way, as well as other distant regions of space, enormous clouds of swirling dust and gas are present. These clouds are classified as nebulae and are the location at which stars are born. Our Solar System was formed from gases and dust that were swirling around the equator of the Sun, with electrostatic forces thought to be responsible for dust particles coalescing to form larger clusters; during this accretion process, clusters then go on to develop into rock formations, which ultimately combine to form massive planetary bodies.
Since they circled the Sun as a single, flat disc, these gases began life in the same plane. With Earth making an orbit of a mere 7.2 degrees relative to the plane of the Sun’s equator, astronomers were astonished to find that some of the planets of distant solar systems orbited at far steeper angles.
A study that was published in the Astronomy & Astrophysics journal, in 2008, led by Guillaume Hébrard, described this unusual phenomenon in extrasolar planet XO-3b. XO-3b is an extrasolar planet that transits its F5V parent star, with an orbital period of just over three days. Similar observations have also been made, by fellow astronomers, when investigating exoplanets HD147506b, HD 17156b and GJ 436b, to name a few examples.
Nonetheless, a group of researchers have, for the first time, discovered a multi-planet system that is tilted out of alignment, but also lacks an interloping “hot Jupiter.” The study was led by Daniel Huber of the NASA’s Ames Research Center, situated at Moffett Federal Airfield in California, with the findings published in the Oct. 18 issue of the journal Science.
Kepler-56 & Transiting Exoplanets
Huber and his colleagues specifically looked at the Kepler-56 star, situated some 3,000 light years from Earth, with a size four times that of the Sun and a mass that is 30 percent greater. This solar system features two confirmed planets – one that is slightly smaller than Jupiter in size and another that is slightly smaller than Saturn. Both of these exoplanets orbit Kepler-56 in the same plane, at a distance from the host star that is smaller than the distance of Mercury from our Sun.
The now defunct Kepler spacecraft collected information as the exoplanets transited across Kepler-56, which impeded emission of some of the star’s light towards Earth.
Kepler was launched by the space agency in 2009 to identify other Earth-like planets, in what astronomers refer to as the habitable zone (a.k.a. the Goldilocks zone). This habitable zone represents the region around a host star where planetary bodies can support liquid water.
Kepler encompasses a photometer, tasked with continuously measuring the brightness of in excess of 140,000 main sequence stars. The information is periodically fed back to ground control teams on Earth, where astronomers attempt to detect transient dimming of individual host stars, resulting from exoplanets moving in front of them.
By observing the change in brightness of Kepler-56 over time, the group were able to determine the precise orbits of the exoplanets.
According to Nature News, Kepler-56 is estimated to emit around nine times more light than the Sun. In attempting to establish the star’s orientation, the Kepler satellite was used to investigate fluctuations in its brightness, which had resulted from its vibrations; the star’s appearance altered, depending upon whether it was witnessed “… equator-on, pole-on or somewhere in between.”
Keck I Discovers a Third, Massive Planet
Ultimately, the work revealed, quite startlingly, that the slant of the rotation axis of Kepler-56 was 45 degrees to the orbit of the exoplanets. In fathoming this extraordinary observation, the astronomers elected to perform follow up studies around Kepler-56. To do this, they used the Keck I telescope, located in Hawaii.
This led to the breakthrough that explained why the solar system was tilted. They found an additional, massive outer planet, whose gravitational pull hauls the orbit of the other two planets away from Kepler-56’s equator.
In spite of this, the two planets are in stable orbit, and remain aligned with each other, due to the difference in the time it takes each planet to make its orbit; as one of the planets orbits the host star at double the time of its sibling, they intermittently nudge one another back in line, as explained by Kawaler:
“It issues a continuous tug on the orbit of the smaller ones, pulling them into their inclined orbits.”
NASA’s Kepler space telescope has managed to, for the very first time, prove that tilted solar systems can exist, even in the absence of hot Jupiters.
By: James Fenner