“Alien Planet” Is an Outsider

The planet, over two-thousand light-years from earth, circles a star known as HIP 13044. At least the size of Jupiter, the planet was discovered by astronomers at the Max Planck Institute for Astronomy and the European Space Agency who noticed a puzzling 16-day fluctuation in HIP 13044’s velocity relative to our own solar system. From that, they inferred the existence of a planet orbiting the star.

They inferred the existence of a planet orbiting the star.

What’s strange about this planet is that it’s in the wrong place, apparently. HIP 13044 is a metal-poor star, with only about one-hundredth as much metal (used in a broad sense to mean heavy elements) as our own sun. Evolutionary views of planet formation postulate that stellar metal is crucial for planet formation, and thus requires stars with plenty of metal—not stars like HIP 13044. So where did the planet come from?

HIP 13044 is located amid a band of stars in our galaxy called the Helmi stream. The stars supposedly originated in another galaxy, having joined the Milky Way when the two galaxies collided between six and nine billion years ago. Given this background, the team has suggested that HIP 13044’s planet—and perhaps the star itself—isn’t from our galaxy at all, and the two became acquainted long after they first formed. “The claim that it’s extragalactic is kind of a guess,” NASA’s Steven Pravdo admits, though he said the idea is “a nice possibility.”

According to Rice University astronomer Christopher Johns-Krull, the planet disputes the idea of gradual, evolutionary planet formation. “This planet says, maybe that’s not right,” he notes, suggesting a more violent process is responsible instead. Either way, HIP 13044’s unexpected planet stands in sharp contrast to standard, naturalistic models of planet formation and shows one of the problems in an evolutionary view of astronomy.