Long before our Sun and Earth existed, or even the Milky Way galaxy, as we know it today, a planet formed around a sun-like star in one of the earliest homesteaders of our corner of the universe, a globular star cluster.

This planet, a few times more massive than Jupiter has survived the harsh conditions of a globular cluster, a gravitational collision with a binary system, and the death of its progenitor star.

The planet resembled Jupiter in several ways: its mass was only a few times that of Jupiter and its orbit was similar, somewhere between 250 and 750 million miles from its sun. The star and planet orbited untouched for almost 10 billion years as they fell into the dense heart of the cluster, where stars are so crowded together they are a fraction of a light-year apart. Like strolling into a crowded marketplace, this star system would not be independent for long without "bumping" into something.

The new system of the planet, its sun, and the neutron star recoiled from the ejected white dwarf, in much the same way a cannon jumps backwards when it fires a cannon ball. This gravitational recoil sent the new binary system out of the globular cluster’s core into a less dense region of the cluster, reducing its chance for another such stellar interaction.

At its new position in the cluster, the planet slowly traced out a wide orbit around the neutron star and its progenitor star at a distance of approximately 2 billion miles, which is similar to Uranus’s orbit around our Sun. From this vantage point the planet witnessed the death of its progenitor star over the course of the next billion years. The sun-like star aged into a red giant and poured matter onto the neutron star. The neutron star’s acquisition of mass caused it to rotate faster and faster on its axis, eventually spinning up into a pulsar. Now the neutron star makes almost 100 rotations per second on its axis (that’s 10 times faster than a humming bird flaps its wings!)

Once all the excess gas left the star, it became a small, bright, helium-core white dwarf. All the while, the planet continued on its sweeping orbit. This is the state, established less than one billion years ago, in which astronomers discovered the planet.

So, how could researchers tell that this planet had survived such dynamic cosmic forces, or existed at all? Using Hubble data, scientists used the white dwarf’s color and temperature to determine its age and mass, which they compared to the wobble of the neutron star. In addition, radio studies of the pulsar revealed irregularities in its signal that could not be caused solely by its white dwarf companion star.

Putting this information together, researchers obtained a tilt for the white dwarf’s orbit, after which they could infer the tilt of the third orbiting body. From there, astronomers were able to determine the mass of the third body, which is too small to be a brown dwarf or a low-mass star; thus, the planet revealed itself through its subtle tug on the system. "We probably would never have found this planet if it had just stayed with its original star," remarked Steinn Sigurdsson of Pennsylvania State University. "Its history put it in the right place; the interactions helped us see it."

Furthermore, the planet’s orbit and place in the globular cluster give us clues to its past. For the proposed scenario to be plausible, the white dwarf must have lost its gaseous envelope after it and the planet joined the neutron star; therefore, the white dwarf should be young, bright, and low mass, which evidence suggests is the case. In addition, the planet’s presence in a wide near-circular orbit reveals that the mass transfer from the progenitor star, now the white dwarf, to the neutron star, spinning up into a pulsar, did occur after the planet was in an orbit around the pair.

The wide orbit also makes the planet more vulnerable to the gravitational forces of nearby stars, in which case the planet’s continuing presence suggests the system has been in the lower-density portion of the cluster since its current configuration was established. Because such a system would return to the cluster’s core on a time scale of a billion years and we know that the system has not yet returned, we can establish the time scale for the current configuration, the tumultuous series of events leading to the present, and an age for the planet.

This planet’s tale also gives astronomers an idea of where planets may reside and how many could exist. The planet was born before many heavier elements existed in space, such as oxygen, carbon and silicon. It’s birth in such an element-poor globular cluster like M4 may imply that planets are more common in such environments than once thought.

"This is a big hint that there are more out there," said Sigurdsson. "There are 100 pulsars like [the one this planet orbits] out there, this one was just extremely well researched."

Having theorized the planet’s existence 10 years ago, Sigurdsson says the discovery of this planet means that we must "overcome theoretical prejudices" and "suggests we should make more of an effort to look for [such planets]." Coming in at 13 billion years old, this planet also makes a case for planet formation occurring earlier and more abundantly than previously thought.