Workshop discovery: Are there other Earth-sized planets in the solar system?

The discovery of a workshop raises the possibility of another Earth-sized planet in the solar system

Our corner of the galaxy changed with the discovery of Sedna, the most distant object discovered in the solar system. Now astronomers wonder how it got there.

The most fascinating idea is that there may be another world, the size of the Earth, a kind of gravitational bully, residing in some hidden corner of the solar system.

The problem with Sadna is this: Scientists can't figure out how Sadna, which is about three-quarters the size of Pluto, completes such a strange orbit around the Sun. The track of a workshop is particularly elliptical. At the point closest to the sun in its orbit, its distance from it is 76 astronomical units (AU), while at the farthest point, its distance from the sun is 1000 astronomical units. An astronomical unit is the distance between the Earth and the Sun.

"How could anything get into such an orbit," wonders astronomer Brian Marsden. He raises the possibility that an Earth-sized planet had a hand in the matter.

Michael Brown, the astronomer from the California Institute of Technology, who led the discovery of Sadna, says that according to the most likely scenario, the Sun was born in a cluster of stars, and some stars, which were closer to the Sun (although their distance was no less than 10,000 astronomical units) are responsible for Sadna's entry to the track

Other astronomers, who were not involved in the discovery of Sadna, also support the idea that Sadna was put into orbit by the influence of another star, but other astronomers do not accept this idea.

"I don't really like it," said Marsden, who heads the Minor Planet Center in Cambridge, Mass., which catalogs new solar system bodies.

Marsden told Space.com that it is leaning toward a closer object, a "planetary object," that is 400 to 1000 AU away.

"There may be more than one planet out there," Marsden said. "who knows? But let's guess something there, whose mass is the mass of the Earth, or several times the mass of the Earth. Approaching such an object may throw Sadna from a more circular orbit to a more eccentric one."

Marsden says that this scenario does not deal with the question of the formation of a body the size of the Earth at such a great distance from the Sun, where according to current theories the raw materials are rare.

Brown said that the possibility of an Earth-sized object exists, but his team's calculations place it at a distance of 70 astronomical units.

"We estimate that it is unlikely, as we think we would have discovered it by now," Brown said in a telephone interview.

Alan Bos, a planet formation theorist at the Carnegie Institution in Washington, agrees that a transiting star or a gas cloud are more likely causes of Sedna's strange orbit. Bose said that "it would be hard to imagine" that an object the size of the Earth would form in such a remote area.

However, Brown said, there is a region of the sky that is about twenty percent of the sky that has not been explored so far. No searches have been conducted in this area for an object the size of the Earth, which orbits the Sun at a distance of about seventy astronomical units and is in the main Milky Way plane of the Solar System. This is a region in the sky of the center of the galaxy. This is a very bright area, and it is difficult to search.

Brown said his team is considering doing that search now.

If Marsden is in the right direction, and there is an Earth-sized planet a few hundred AU away, the measurements made so far could easily miss.

In any case, even if such an object is found, it will not be similar to the Earth that we know. Any object beyond Pluto would be a solid block of ice and definitely not a suitable candidate for sustaining life.

There is also another debate. Astronomers disagree on whether Sadna should even be defined as a planet. Many claim that Pluto itself was never entitled to the title of a planet, since it is more similar to Sedna and other objects beyond Neptune, which are small objects and have a particularly elliptical orbit.

In fact, there is no astronomical definition for the term "planet", but the International Astronomical Union clarified in recent years that Pluto, despite the opinion of most astronomers, will continue to bear the title "planet". We don't know what to call an object the size of the Earth, orbiting the Sun in a circular orbit beyond Neptune, but it would be hard not to consider it a planet.

Alan Stern of the Southwest Research Institute adds another complication to the plot. Stern thinks that Earth-sized planets may exist in the Oort Cloud, the most distant region of the solar system.

Brown's team said they believe Sadna should be considered the first known object from the Oort Cloud, whose existence is otherwise only theoretical. They hypothesized the existence of this pool of small, icy objects based on the orbits of several comets, which occasionally approach the solar system and disappear back into space.

However, no one knows what is really in the Oort cloud.

"I would say that this possibility is plausible," says Stern regarding the possibility of the existence of Earth-sized planets in the Oort cloud. In the early days of the solar system, explained Stern, it is estimated that objects the size of the Earth hit Uranus and Neptune. Computer simulations show that most of these objects, if they did exist, "would be ejected outside the region of the outer planets and not remain in the region of Uranus and Neptune, so we could one day find these frozen remains in the Oort cloud."

The search for worlds at such vast distances will surely be a huge challenge. It is estimated that the Oort cloud extends almost to half the distance to the nearest star.

Link to the article on Space.com