Tag Archives: planetary formation

Mid-Sized Planetary Body in Kuiper Belt Could Float In Water

Planetary scientist Michael Brown from CalTech has measured the density of a planetary body in the Kuiper Belt that is over 400 miles (650 km) wide – and he found that it has a lower density of than water. This is the largest rock discovered in the solar system which would be capable of floating. Brown published the results in The Astrophysical Journal Letters, which appeared online this week.

The body is known as 2002 UX25 and may shake up current theories about how planetary bodies are formed, as it is the first mid-sized body measured for density. Traditionally, it has been believed that planetary bodies were formed by bits of dust whipping around the sun in its infancy. Eventually, the dust particles slammed into one another to form larger rocks. It has been thought that all of the rocky planets formed this way, along with all of the planetary bodies in the Kuiper Belt at the edge of the solar system.

However, if that model was entirely correct then all of the bodies in the Kuiper Belt should have roughly the same density. In fact, smaller bodies are reported to be less dense than water. This was thought to have been reconciled by the idea that the larger rocks have a greater gravitational pull and bring the dust in closer and tighter. Since 2002 UX25 is mid-sized and has a density more similar to a small body instead of one halfway between the small and large as would be expected, there might be something else going on.

Because 2002 UX25 only has a density of about 0.8 grams per cubic centimeter, it is assumed that it contains a great deal of ice. This allowed other planetary scientists to propose a new theory of planetary formation: the solar system was made from the outside in. As the dust flew around creating small rocks, it collected a lot of ice. Larger rocks that had been hit many times had some of the ice knocked out of them, creating a more dense, larger rock. The largest of the proto-planets were drawn inward toward the sun, while the icy remnants remained out at the Kuiper Belt. 

It’s an interesting thought, but several other 2002 UX25-sized planetary bodies will need to be measured before strong assertions of a new theory for formation can be made.

Read more: http://www.iflscience.com/space/mid-sized-planetary-body-kuiper-belt-could-float-water

Massive Asteroids Battered Early Earth

It’s common knowledge that the early solar system was a fairly inhospitable place, as massive rocks continuously slammed together for millions of years, eventually creating planets. New research has indicated that during the first 500 million years of Earth’s history, huge asteroids bombarded the planet, causing drastic mixing and reshaping of the surface, which explains why we don’t have samples of those earliest rocks. The research was completed through an international collaboration and the paper was published in Nature

Our solar system began to form roughly 4.5 billion years ago. As the dust and gas coalesced into progressively larger rocks that slammed into one another, the rocks that would eventually be known as Earth went through several phases of bombardment that shaped the planet as we see it today. Shortly after the Earth was formed, it collided with a planetary body roughly the size of Mars and generated the debris that would form our moon. Later, it got pelted with asteroids so large, they made the one that wiped out the dinosaurs look like a pebble. 

The Hadean geological eon represents everything that happened prior to four billion years ago. The asteroid collisions near the end of this period did not add a lot of mass to Earth, but were powerful enough to bury or melt some of the earliest rocks on the surface. Additionally, the heat generated from the impacts may have boiled entire oceans, creating a heavy, humid atmosphere multiple times. Previous studies have indicated that water has been on Earth for about 4.3 billion years, and this model does support that claim.

“Prior to approximately four billion years ago, no large region of Earth’s surface could have survived untouched by impacts and their effects,” lead author Simone Marchi said in a press release. “The new picture of the Hadean Earth emerging from this work has important implications for its habitability.”

So how big were these asteroids? According to this model, as many as four could have been over 600 miles wide while around 3-7 were closer to 300 miles wide. For a size comparison, the asteroid that hit 65 million years ago was around 6 miles wide. Life is believed to have originated within the first billion years of Earth’s history and could have been greatly affected by these impacts. The larger asteroids may have been capable of incinerating life all around the planet, while the smaller ones would have been enough to turn entire oceans into steam. However, these collisions were spaced out and allowed for conditions to settle down.

“During that time, the lag between major collisions was long enough to allow intervals of more clement conditions, at least on a local scale,” said Marchi. “Any life emerging during the Hadean eon likely needed to be resistant to high temperatures, and could have survived such a violent period in Earth’s history by thriving in niches deep underground or in the ocean’s crust.”

Size and location of craters by asteroids, color-coded by time of impact. Image Credit: Simone Marchi et al. 2014

Read more: http://www.iflscience.com/environment/massive-asteroids-battered-early-earth

ALMA Spots Double Star With Bizarre Planet-Forming Discs

Binary stars are fairly common throughout the Universe, but astronomers have puzzled over how these stellar pairs can form planetary systems. Some of these questions are receiving answers due to observations made by the ESO’s Atacama Large Millimeter/submillimeter Array (ALMA). Most notably, it was revealed that the planet-forming discs surrounding each star in the HK Tauri binary star system are massively misaligned. The research was performed by Eric Jensen of Swarthmore College in Pennsylvania and Rachel Akeson of NASA’s Exoplanet Science Institute at CalTech, and the paper will be published in Nature.

Located 450 light-years away in the constellation Taurus, HK Tauri consists of a pair of 5 million year old stars that are separated by a distance about 13 times greater than Neptune and our Sun. These baby stars are surrounded by clouds of dust and gas that are being swirled around due to gravity, forming flat discs. The swirling dust will begin to stick together, and over time form members of a planetary system. 

HK Tauri A is the brighter of the two, and the glare washes out much of the protoplanetary disc surrounding it which required the disc to be imaged in millimeter-wavelength light. HK Tauri B’s disc is oriented so that we see it on its edge. This dust cuts blocks a lot of the brightness from the star, allowing the disc to be imaged at visible and near-infrared wavelengths. Although, the fact that the pair of stars have planet-forming discs that are on different planes by a staggering 60 degrees was a surprising insight into planetary formation.

“This clear misalignment has given us a remarkable look at a young binary star system,” Akeson said in a press release. “Although there have been earlier observations indicating that this type of misaligned system existed, the new ALMA observations of HK Tauri show much more clearly what is really going on in one of these systems.”

As HK Tauri is a binary system, typical planetary formation gets confounded. The vast misalignment of the disc planes could lead to highly unusual orbits because of gravitational pull from the companion star. This could lead to planets that precess, which is when the planet’s axis also has an axis which it spins around (sort of like when a spinning top gets wobbly before it falls). Preliminary analysis indicates that the conditions in this system could very well be enough to interfere with those future orbits. 

Astronomers have never before been able to witness a binary system at this early stage in planetary formation, and more research is needed to determine if the misalignment seen in HK Tauri is standard or not. 

“Although understanding this mechanism is a big step forward, it can’t explain all of the weird orbits of extrasolar planets — there just aren’t enough binary companions for this to be the whole answer. So that’s an interesting puzzle still to solve, too!” Jensen added.

Read more: http://www.iflscience.com/space/alma-spots-double-star-bizarre-planet-forming-discs