Category: Solar System

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There’s a new spacecraft in Earth orbit, with a really “far out” mission: to map the outer solar system. NASA’s Interstellar Boundary Explorer mission, or IBEX launched successfully from the Kwajalein Atoll in the Pacific Ocean at 1:47 p.m. EDT, Sunday, from an Orbital Sciences Pegasus XL launch vehicle. IBEX will be the first spacecraft to image and map dynamic interactions taking place in the outer solar system. The two Voyager probes sent back a limited amount of information about the region of space where our solar system ends and interstellar space begins. But beyond that, not much is known about this area. The region is about three times further from the sun than the orbit of planet Pluto. “No one has seen an image of the interaction at the edge of our solar system where the solar wind collides with interstellar space,” said IBEX Principal Investigator David McComas of the Southwest Research Institute in San Antonio. “We know we’re going to be surprised.”

The spacecraft separated from the third stage of its Pegasus launch vehicle at 1:53 p.m. and immediately began powering up components necessary to control onboard systems. The operations team is continuing to check out spacecraft subsystems.

“After a 45-day orbit raising and spacecraft checkout period, the spacecraft will start its exciting science mission,” said IBEX mission manager Greg Frazier of NASA’s Goddard Space Flight Center in Greenbelt, Md.

“The heliosphere’s boundary region is enormous, and the Voyager crossings of the termination shock, while historic, only sampled two tiny areas 10 billion miles (16 billion km) apart,” NASA scientist Eric Christian said.

Voyager 1 passed the inner boundary in 2004 and Voyager 2 crossed over last year.

The solar wind, a stream of electrically conducting gas continuously moving outward from the sun at 1 million mph (1.6 million kph), blows against this interstellar material and forms a huge protective bubble around the solar system. This bubble is called the heliosphere.

As the solar wind reaches far beyond the planets to the solar system’s outer limits, it encounters the edge of the heliosphere and collides with interstellar space. A shock wave is present at this boundary.

“Every six months, we will make global sky maps of where these atoms come from and how fast they are traveling. From this information, we will be able to discover what the edge of our bubble looks like and learn about the properties of the interstellar cloud that lies beyond the bubble,” physicist Herb Funsten of the U.S. Department of Energy’s Los Alamos National Laboratory.

Sources: NASA, Reuters

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A group of astronomers spent two years photographing portions of the sky to look for small chunks of rock and ice orbiting beyond Neptune, in the Kuiper Belt region of our Solar System. The survey targeted Kuiper Belt objects (KBOs) with sizes between 2 miles (3 km) and 17 miles (28 km). The researchers are surprised, as well as a little disappointed with the results. They came up empty. Nada. Not a single KBO within those parameters was spotted. But these researchers from the Taiwanese-American Occultation Survey (TAOS) are ‘glass-half-full’ types, and say that defeat can provide as much information as a successful search, so they are making the most of their data. What this means is that there are less KBOs out there than previously thought.

Since the KBO’s this group searched for are too small to see directly, the survey watched for stars to dim as KBOs passed in front of and occulted them. After accumulating more than 200 hours of data watching for stellar flickers lasting a second or less, TAOS did not spot any occultations.

Here’s a movie that illustrates their search.

The Kuiper Belt contains objects in a range of sizes: a few very large ones (like the dwarf planets Pluto, Eris, Makemake and Haumea) and many more smaller ones. The commonness of a given size tells us information about the history of planet formation and dynamics. In particular, the size distribution of KBOs reflects a history of agglomeration, in which colliding objects tended to stick together, followed by destructive collisions, where collisional velocities were high enough to shatter the rocks involved.

Astronomers questioned whether they would find more and more objects as sizes decreased further, or whether the distribution leveled out. The fact that no occultations were seen sets a stringent upper limit on the number density of KBOs between 2 and 17 miles in diameter. The outer solar system, therefore, appears not as crowded as some theories suggest, perhaps because small KBOs have already stuck together to form larger bodies or frequent collisions have ground down small KBOs into even smaller bits below the threshold of the survey.

The paper announcing this result, co-authored by CfA director Charles Alcock, was published in the October 1 issue of the Astrophysical Journal Letters.

Sources: TAOS, CfA

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What prompted the formation of our little corner of the universe – our sun and planetary system? For several decades, scientists have thought that the Solar System formed as a result of a shock wave from an exploding star—a supernova—that triggered the collapse of a dense, dusty gas cloud, which then contracted to form the Sun and the planets. But detailed models of this formation process have only worked under the simplifying assumption that the temperatures during the violent events remained constant. That, of course, is very unlikely. But now, astrophysicists at the Carnegie Institution’s Department of Terrestrial Magnetism (DTM) have shown for the first time that a supernova could indeed have triggered the Solar System’s formation under the more likely conditions of rapid heating and cooling. So have these new findings resolved this long-standing debate?

“We’ve had chemical evidence from meteorites that points to a supernova triggering our Solar System’s formation since the 1970s,” remarked lead author, Carnegie’s Alan Boss. “But the devil has been in the details. Until this study, scientists have not been able to work out a self-consistent scenario, where collapse is triggered at the same time that newly created isotopes from the supernova are injected into the collapsing cloud.”

Short-lived radioactive isotopes—versions of elements with the same number of protons, but a different number of neutrons—found in very old meteorites decay on time scales of millions of years and turn into different (so-called daughter) elements. Finding the daughter elements in primitive meteorites implies that the parent short-lived radioisotopes must have been created only a million or so years before the meteorites themselves were formed. “One of these parent isotopes, iron-60, can be made in significant amounts only in the potent nuclear furnaces of massive or evolved stars,” explained Boss. “Iron-60 decays into nickel-60, and nickel-60 has been found in primitive meteorites. So we’ve known where and when the parent isotope was made, but not how it got here.”

Previous models by Boss and former DTM Fellow Prudence Foster showed that the isotopes could be deposited into a pre-solar cloud if a shock wave from a supernova explosion slowed to 6 to 25 miles per second and the wave and cloud had a constant temperature of -440 °F (10 K). “Those models didn’t work if the material was heated by compression and cooled by radiation, and this conundrum has left serious doubts in the community about whether a supernova shock started these events over four billion years ago or not,” remarked Harri Vanhala, who found the negative result in his Ph.D. thesis work at the Harvard-Smithsonian Center for Astrophysics in 1997.

Using an adaptive mesh refinement hydrodynamics code, FLASH2.5, designed to handle shock fronts, as well as an improved cooling law, the Carnegie researchers considered several different situations. In all of the models, the shock front struck a pre-solar cloud with the mass of our Sun, consisting of dust, water, carbon monoxide, and molecular hydrogen, reaching temperatures as high as 1,340°F (1000 K). In the absence of cooling, the cloud could not collapse. However, with the new cooling law, they found that after 100,000 years the pre-solar cloud was 1,000 times denser than before, and that heat from the shock front was rapidly lost, resulting in only a thin layer with temperatures close to 1,340°F (1000 K). After 160,000 years, the cloud center had collapsed to become a million times denser, forming the protosun. The researchers found that isotopes from the shock front were mixed into the protosun in a manner consistent with their origin in a supernova.

“This is the first time a detailed model for a supernova triggering the formation of our solar system has been shown to work,” said Boss. “We started with a Little Bang 9 billion years after the Big Bang.”

Source: Carnegie Institution for Science