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Did the Sun Eat a Primordial Super-Earth?

Was there a so-called 'super-Earth' planet that formed inside the orbit of Mercury? If so, it might have been eaten by our sun.

A new study suggests that at least one super-Earth - a planet that is larger than Earth, but smaller than Neptune - could have formed close to the sun. Over time, this hypothetical super-Earth would have swept up all the debris in the area. Then, it would have succumbed to the sun's gravity and gotten eaten.

PHOTOS: Hubble's Backyard: Our Solar System

This could be a possible explanation for why nothing is seen within the orbit of Mercury, although for now the evidence is based on modelling and the fact that the region between Mercury and the sun is so barren, the authors say.

"The only (physical) evidence that super-Earths could have formed in our solar system is the lack of anything in that region, not even a rock," said lead author Rebecca Martin, an assistant professor at the University of Nevada, Las Vegas, in an email to Discovery News. "So they could have formed there sweeping up all of the solid material, but then later fell into the sun."

ANALYSIS: Jupiter May Have Killed Solar System's Baby Super-Earths

Observations of super-Earth exoplanets outside the solar system suggest they could have formed in two locations: in situ (where you see them today) or farther out from their observed locations, where of course they would have migrated over time.

Mercury transits the sun as seen by the Solar and Heliospheric Observatory in 2006. Credit: Mercury transits the Sun as seen from Earth in 2006. | ESA/NASA/SOHO

For them to be formed in situ, the super-Earths would have to slowly build up from debris in the "dead zone" of a forming planetary system, known as a protoplanetary disc. This would only happen if there is a lot of turbulence in this area, fueled by magnetism of the surrounding material.

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"The size of the dead zone must be large enough that it lasts for the entire disc lifetime," Martin added. "Since different systems may have different dead zone sizes, formation in the inner parts may not be possible in all systems and thus both formation locations may be operating."

Of the super-Earths that have been observed, the researchers noted two distinct types depending on their density. They conclude that planets that form farther out in the disc would be less dense, since water and other volatiles will freeze out in the cooler outer parts of the disc. Those that are closer one would be denser.

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So what about our own solar system? The researchers speculate that here, super-Earths formed in situ and swept up all the material inside of Mercury's orbit. "If the disc is sufficiently cool, the migration timescale for them to fall into the sun is short enough for this to happen in the lifetime of the disc," Martin said. But more research will be needed to confirm this.

The research was accepted for publication in the Astrophysical Journal, and is now available in preprint version on Arxiv.

Artist’s impression of the super-Earth Kepler-69c.

As part of Science Channel Weekend,

Discovery Channel will premiere "Telescope" on Feb. 20 at 9 p.m. ET/PT

, a "dynamic journey behind the scenes of the next step in the evolution of telescopes: NASA's James Webb Space Telescope," directed by Oscar®-nominated filmmaker Nathaniel Kahn. This next-generation telescope will be 100 times more powerful than the NASA/ESA Hubble Space Telescope, but Hubble, which has been observing the cosmos for quarter of a century, continues to dazzle us with stunning views of the universe. However, some of its most beautiful observations are right here in Hubble's backyard.

Hubble's Recent Discoveries and Stunning Photos

As we get excited for the next generation in space telescopes and what awesome views of the distant cosmos they will bring, let's return home, to our solar system. Here's a small selection of our favorite planets, asteroids, comets and moons that Hubble has studied in recent years.

The Red Planet is a Hubble favorite and, depending on where it is in its orbit, the space telescope

will check in periodically

. Our solar system neighbor can be seen very clearly by Hubble, which can also see atmospheric changes such as global dust storms.

Deep inside the asteroid belt that occupies the space between the orbits of Mars and Jupiter lurks a massive asteroid and long before NASA's Dawn mission slid into orbit around Vesta,

Hubble was on hand to zoom in on the small world


Although rare, Hubble has been able to image its fair star of asteroids that are literally falling apart.

In this series of observations

(starting in late 2013), an asteroid breaks up, not due to an impact, but through interactions with sunlight that caused the rocky obect to "spin up" and rip itself to shreds.

MORE: Hubble Witnesses Mysterious Breakup of Asteroid

Hubble has evened challenged the distinction of what's a comet and what's an asteroid. Shown here is an object

that has the attributes of both

-- it is known as an "active asteroid," which is generating its own comet-like tail. As Spock would say: "



MORE: Dying Space Rock: Asteroid-Comet Hybrid Discovered

Hubble is also a very seasoned comet hunter and has proven itself proficient at tracking some of the biggest cometary events of our time. One such recent event was the stunning inner solar system encounter with Comet ISON that received international attention for being a potentially bright comet that could outshine the moon. Sadly, the icy vagabond never lived up to its potential and ultimately got fried by the sun, but at least Hubble captured its portrait before it was vaporized.

You may remember the

dramatic break-up of Comet Shoemaker-Levy 9 in 1994

that ended up as the mother of all planetary impacts in the atmosphere of Jupiter, but since then Hubble has had a ringside seat of a few more Jovian punches. Following up on amateur astronomers' observations of a weird bruise on Jupiter,

Hubble took a closer look in 2009

to see an impact feature that looked strikingly similar to the aftermath of Shoemaker-Levy 9. These observations by Hubble have helped scientists begin to understand just how common energetic planetary impacts are in our modern solar system.

During an extended campaign last year,

Hubble took several high-resolution observations

of the solar system's biggest planet, Jupiter. In the stunning upper atmosphere maps of the gas giant, previously unnoticed waves were seen. Also, astronomers took note of the size of Jupiter's shrinking "Great Red Dot."

MORE: Hubble's Jupiter Maps Reveal Weird Structures

In 2009, ringed gas giant Saturn was aligned with Earth and Hubble took the opportunity to not only observe the edge-on rings, but to also observe aurorae rumbling in the northern and southern magnetic poles. This was an amazing scientific boon to learn about solar wind activity at both poles simultaneously,

but it also made for some beautiful imagery


MORE: Saturn's Aurora Could Hold Key to Radio Pulse Mystery

If a planet has a magnetic field and it is hit by a dose of space weather, there's the potential of some aurora. This is true for Earth and, as proven by Hubble, this is true of other planets in the solar system too. Though the aurorae of Saturn and Jupiter often take center stage,

these 2011 observations show

elegant auroral activity in the upper atmosphere of Uranus, the solar system's strangely tilted ice giant planet.

MORE: Hunting Uranus, the Solar System's Azure Ice Giant

From its privileged orbital perch, Hubble can even discover tiny moons orbiting the outer solar system planets.

Shown here

is the discovery observation of Neptune's moon S/2004 N 1 that was found by astronomers poring over archival Hubble imagery of the ice giant planet.

MORE: Diamond Oceans Possible on Uranus, Neptune

Although mottled and blurry, before NASA's New Horizons mission flew past Pluto on July 14, 2015, this was the best view we had of Pluto, as seen through Hubble's lens. Still, the space telescope was able to decipher

different toned landscapes

and even atmospheric dynamics from afar.

MORE: Fuzzy to Clear: Space Robots Snap Solar System Into Focus

During its decade-long coast to the outer solar system, NASA's New Horizons mission was assisted by Hubble in many ways. Principally, Hubble was used to seek out previously undiscovered moons orbiting the dwarf planet. Not only is it cool to discover new things in the outer solar system, this observation campaign would eventually help New Horizons scientists work out if the Pluto system was a dangerous place filled with potential spacecraft-smashing debris. In the process of this campaign, Hubble discovered "P4" and "P5" that were eventually called (after an entertaining public vote and debate) Kerberos and Styx.

MORE: Pluto's Moons Offer Secrets and Threaten Danger

When NASA's New Horizons mission flew past Pluto on July 14, 2015, it wasn't destined to be a one-trick pony; mission scientists had plans for it to visit another outer solar system object, deep within the Kuiper Belt, sometime in 2019. Hubble had a huge role to play in this extended mission decision, helping astronomers survey the depths of the Kuiper Belt to eventually find the perfect candidate: a mysterious body called 2014 MU69 (PT1).

This observation

shows 2 candidate Kupier Belt objects that were considered in 2014 before the probe's Pluto encounter.

MORE: Pluto Probe Spies Object Lurking in the Kuiper Belt