Tag Archives: dwarf star

Credit: Lucasfilm

More than a million years from now, our solar system will briefly house two stars

A double sunset such as the fictitious one on Tatooine from Star Wars has always been on many people’s minds. About 1.3 million years from now, if anyone is still around, he could actually experience a similar scenery here on Earth.

Credit: Lucasfilm

Credit: Lucasfilm

Uninvited stellar guests

Nothing is static in the Universe. Though our senses tell us we’re standing still, since the days of Copernicus we’ve known that the planet we call home revolves around the Sun, which in turn moves around the center of Milky Way, which yet again revolves around the center of mass lying in between Andromeda and Milky Way. In other words, everything is in perpetual motion relative to a reference point. This means that sometimes cosmic objects and systems can behave in very surprising ways.

A massive survey of 300,000 stars and their motion relative to the Sun was performed by astronomers working with the ESA’s Gaia satellite. The scientists plotted the stars’ closest approach to the Sun determined for up to five million years in the past and future. They found 97 stars which should pass within 150 trillion kilometers, with 16 coming within about 60 trillion km.

A particular encounter stands out, that with Gliese 710, which will pass within just 2.3 trillion km or about 16 000 Earth–Sun distances, some about 1.3 million years from now. For a sense of measure, the outermost planet of the solar system, Neptune, orbits around the sun at 30 Sun–Earth distances.

That puts Gliese 710 well within the Oort Cloud, a humongous shell of icy objects that exist in the outermost reaches of the solar system, extending out to 15 trillion kilometers from the Sun or 100 000 times the Sun–Earth distance.

Understanding alien stars that approach our solar system is important work that might one day even avert a planetary catastrophe. It’s thought that most comets in our solar system come from the Oort Clouds. These are mainly perturbed by the gravitational influence of stars which jolts them into orbits that bring the comets closer to the inner solar system. Some of these comets could enter a collision course with Earth or other planets.

Coming this close to the sun, Gliese 710 will certainly stir the Oort Cloud bee-hive, though in what way remains unclear at this point.

We do know that this alien star has a mass of 60% that of our Sun and that it travels much slower than most stars: nearly 50 000 km/h at closest approach, compared with the average 100 000 km/h. This relatively slow motion will likely amplify the Oort Cloud perturbation effect than otherwise in the case of faster stars.

What’s also certain is that Gliese 710 will shine brightly in the night’s sky as seen from Earth’s surface. Astronomers estimate its brightness will be three times that of Mars.

Meeting a rogue

The following animation put together by ESA focuses on Gliese 710 wandering through the galaxy, ultimately performing a close encounter with our Sun in 1.3 million years by passing within the Oort Cloud reservoir of comets in the outskirts of our Solar System. The ESA’s press release explains further that:

“The motion can be likened to what an observer standing beside a road would see looking at an approaching car, and then swinging around to continue to follow it as it moves away. As a result, the objects in the background – in this case distant stars – become blurred as you move quickly to maintain a visual on the passing object.”

Of course, Gliese 710 wouldn’t be the first star to cause a racket in our solar system’s backyard. About 70,000 years ago, during a time when our ancestors were busy staying alive in the aftermath of the Toba super-eruption, a low-mass star system nicknamed “Scholz’s star” passed roughly 52,000 astronomical units away from the sun.

Scientific reference: “The completeness-corrected rate of stellar encounters with the Sun from the first Gaia data release,” by C.A.L. Bailer-Jones, is published in Astronomy & Astrophysics.

Artist impression of KOI-314c. Credit: C. Pulliam & D. Aguilar (CfA)

Newly found gassy exoplanet has mass similar to Earth’s

Artist impression of KOI-314c. Credit: C. Pulliam & D. Aguilar (CfA)

Artist impression of KOI-314c. Credit: C. Pulliam & D. Aguilar (CfA)

A team of astronomers recently discovered a new exoplanet some 200 light years away whose mass is about the same as Earth’s – the first Earth-mass planet that transits, or crosses in front of, its host star. Although very similar in mass, the planet is 60% larger in diameter suggesting it has a thick atmosphere. Due to its very short orbital period, the planet’s surface is most likely scorching hot and, consequently, unfit to foster life.

Astronomers used data from NASA’s Kepler spacecraft, now defunct, to identify the exoplanet KOI-314c, which orbits a dwarf star. Considering the exoplanet is very far away from Earth and it orbits a very faint star, describing KOI-314c in terms of mass and size was no easy task.

Typically, scientists rely on fairly straightforward method for determining the mass of planets outside our solar system that relies on studying wobbles of the parent star induced by the planet’s gravity. This only works accurately for big planets, at least 1.5 times the size of Earth, that orbit bright stars. For KOI-314c, the researchers used a different technique.

A new method for finding low-mass exoplanets

Known as transit timing variations (TTV), the method, which works only for systems with at least two planets, measures the slight tug planets make on each other, that slightly changes the times that they transit their star.

“Rather than looking for a wobbling star, we essentially look for a wobbling planet,” explains second author David Nesvorny of the Southwest Research Institute (SwRI). “Kepler saw two planets transiting in front of the same star over and over again. By measuring the times at which these transits occurred very carefully, we were able to discover that the two planets are locked in an intricate dance of tiny wobbles giving away their masses.”

Thus, the researchers found KOI-314c is only 30 percent denser than water. This suggests that the planet is enveloped by a significant atmosphere of hydrogen and helium hundreds of miles thick. It might have begun life as a mini-Neptune and lost some of its atmospheric gases over time, boiled off by the intense radiation of its star. The team estimates its temperature is 220 degrees Fahrenheit, too hot for life as we know it.

The second planet, KOI-314b, is about the same size as KOI-314c but much denser, weighing about 4 times as much as Earth. It orbits the star every 13 days, meaning it is in a 5-to-3 resonance with the outer planet.

The TTV method was used for the first time in 2010, and these latest findings show that it can be particularly useful when studying low-mass exoplanets. However, it seems to be effective only when discussing systems with multiple planets. For those of you interested, I invite you read about a new exoplanet hunting technique I wrote about a while ago. Called MassSpec, this method employs transmission spectroscopy – concentrating on measuring light from a star passing through an exoplanet’s atmosphere – and is reportedly accurate for studying the mass of exoplanets that are both low mass and orbit a faint parent star.