Archive for solar system

Asteroid 2015 BZ509 captured from outside the Solar System ~4.5 Gyr ago

Posted in astronomy with tags , on May 21, 2018 by Tim Kendall

Image credit: C. Veillet/Large Binocular Telescope Observatory and text: Sciencemag: Asteroid 2015 BZ509, orbiting close to Jupiter but in a retrograde direction, has probably been in a stable orbit for almost the whole lifetime of the Solar System, it has been found. Its retrograde orbit means it was highly unlikely to be part of the precursor proto-solar nebula, and must have been captured by gravitational interaction with newly-formed massive Jupiter. This and the age of 2015 BZ509 means it is the first object permanently resident in the Solar System to have been identified as possibly originating by capture from interstellar space:

Astronomers first spotted the object, an asteroid called 2015 BZ509 that is orbiting close to Jupiter, in 2014. They knew it was unusual because it was traveling around the solar system in the opposite direction as almost everything else. (Its motion is shown in the animations above, with 2015 BZ509 circled.) Astronomers have found other objects in “retrograde” orbits, perhaps knocked off course by passing too close to a giant planet, but 2015 BZ509’s orbit was the weirdest of all because it is also elongated and out of alignment with the planets and other bodies.

To find out why, a pair of astronomers ran a series of 1 million simulations of the asteroid’s orbit, each with slightly different parameters. Jupiter’s orbit is a busy part of the solar system where the risk of being knocked off course is high, so eccentric orbits that are stable long term are unlikely. But the researchers found a number of possible orbits that were stable and concluded it is much more likely that 2015 BZ509 is in one of them, rather than that it happened to arrive for a short-term visit. Some of those stable orbits, if wound back in time, would mean that 2015 BZ509 has been with us since the beginning of our solar system, about 4.5 billion years ago.

The story has been covered today in the Guardian: “Asteroid from another star system found orbiting wrong way near Jupiter: For the first time, a permanent member of our solar system has been found to have originated elsewhere”, 21 May 2018.

Update: the story has now been covered in more depth by Scientific American, 22 May 2018, and (24 May) the preprint abstract is now available here.

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Saturn near opposition, observed from Earth

Posted in astronomy with tags on June 24, 2017 by Tim Kendall

This view of Saturn from Earth has been taken at the Pic du Midi Observatory, France, which is known for episodes of truly excellent seeing. This is why features can be discerned such as inner faint rings and Saturn’s polar hexagon, which are normally visible only from space probes such as Cassini. Image Credit & Copyright: D. Peach, E. Kraaikamp, F. Colas, M. Delcroix, R. Hueso, G. Therin, C. Sprianu, S2P, IMCCE, OMP and APOD:

Saturn reached its 2017 opposition on June 16. Of course, opposition means opposite the Sun in Earth’s sky and near opposition Saturn is up all night, at its closest and brightest for the year. This remarkably sharp image of the ringed planet was taken only days before, on June 11, with a 1-meter telescope from the mountain top Pic du Midi observatory. North is at the top with the giant planet’s north polar storm and curious hexagon clearly seen bathed in sunlight. But Saturn’s spectacular ring system is also shown in stunning detail. The narrow Encke division is visible around the entire outer A ring, small ringlets can be traced within the fainter inner C ring, and Saturn’s southern hemisphere can be glimpsed through the wider Cassini division. Near opposition Saturn’s rings also appear exceptionally bright, known as the opposition surge or Seeliger Effect. Directly illuminated from Earth’s perspective, the ring’s icy particles cast no shadows and strongly backscatter sunlight creating the dramatic increase in brightness. Still, the best views of the ringed planet are currently from the Saturn-orbiting Cassini spacecraft. Diving close, Cassini’s Grand Finale orbit number 9 is in progress.

Strong evidence suggests a super-Earth lies beyond Pluto

Posted in astronomy with tags , , , on January 24, 2016 by Tim Kendall

45-p9_kbo_extras_orbits_2_

Burdick-Discovering-Planet-Nine-chart-1200Caltech researchers have found evidence of a giant planet tracing a bizarre, highly elongated orbit in the outer solar system. The object, which the researchers have nicknamed Planet Nine, has a mass about 10 times that of Earth and orbits about 20 times farther from the sun on average than does Neptune (which orbits the sun at an average distance of 2.8 billion miles). In fact, it would take this new planet between 10,000 and 20,000 years to make just one full orbit around the sun. A consequence of Planet Nine is that six distant Kuiper belt objects (magenta) all follow elliptical orbits that point in the same direction in physical space; they have the same argument of perihelion. That is particularly surprising because the outermost points of their orbits move around the solar system, and they travel at different rates. A second predicted consequence of Planet Nine is that a second set of confined objects should also exist. These objects are forced into positions at right angles to Planet Nine and into orbits that are perpendicular to the plane of the solar system. Five known objects (cyan, upper figure) fit this prediction precisely. The Sun is at centre in both plots. Credit: Caltech/R. Hurt (IPAC) [Diagram was created using WorldWide Telescope.]

The researchers, Konstantin Batygin and Mike Brown, discovered the planet’s existence through mathematical modeling and computer simulations but have not yet observed the object directly. “This would be a real ninth planet,” says Brown, the Richard and Barbara Rosenberg Professor of Planetary Astronomy. “There have only been two true planets discovered since ancient times, and this would be a third. It’s a pretty substantial chunk of our solar system that’s still out there to be found, which is pretty exciting.” Brown notes that the putative ninth planet—at 5,000 times the mass of Pluto—is sufficiently large that there should be no debate about whether it is a true planet. Unlike the class of smaller objects now known as dwarf planets, Planet Nine gravitationally dominates its neighborhood of the solar system. In fact, it dominates a region larger than any of the other known planets—a fact that Brown says makes it “the most planet-y of the planets in the whole solar system.” Batygin and Brown describe their work in the current issue of the Astronomical Journal and show how Planet Nine helps explain a number of mysterious features of the field of icy objects and debris beyond Neptune known as the Kuiper Belt. “Although we were initially quite skeptical that this planet could exist, as we continued to investigate its orbit and what it would mean for the outer solar system, we become increasingly convinced that it is out there,” says Batygin, an assistant professor of planetary science. “For the first time in over 150 years, there is solid evidence that the solar system’s planetary census is incomplete.” [more]

Further reading: could you live on Planet Nine? (at wired.com) and also see this article at the New Yorker, from which is taken the second graphic (above).