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Monthly Archives: September 2013

NASA’s Voyager 1 spacecraft is officially the first human-made object to venture into interstellar space. The 36-year-old probe is about 12 billion miles (19 billion kilometers) from the Sun.


Credit: NASA/JPL-Caltech

New and unexpected data indicate Voyager 1 has been traveling for about one year through plasma, or ionized gas, present in the space between stars. Voyager is in a transitional region immediately outside the solar bubble, where some effects from our sun are still evident. A report on the analysis of this new data, led by Don Gurnett and the plasma wave science team at the University of Iowa, Iowa City, is published in the journal Science.

Voyager 1 does not have a working plasma sensor, so scientists needed a different way to measure the spacecraft’s plasma environment to make a definitive determination of its location. A coronal mass ejection, a massive burst of solar wind and magnetic fields, that erupted from the Sun in March 2012 provided scientists with the data they needed. When this blast from the Sun eventually overtook Voyager 1 some 13 months later, in April 2013, the plasma around the spacecraft began to vibrate like a violin string. On April 9, Voyager 1’s plasma wave instrument detected the movement. The pitch of the oscillations helped scientists determine the density of the plasma. The particular oscillations meant the spacecraft was bathed in plasma more than 40 times denser than what they had encountered in the outer layer of the heliosphere. This density is that which is expected in interstellar space.

Much more information is available on NASA’s Voyager page, and via this JPL press release, which includes more images and a short video. The sound of interstellar space may be heard here.

Scientists at the Max Planck Institute for Extraterrestrial Physics in Germany have produced the first detailed three-dimensional map of the stars that form the inner regions of our Milky Way, the nuclear bulge (see p. 389).

Credit: ESO/NASA/JPL-Caltech/M. Kornmesser/R. Hurt

Using publicly available data from ESO’s VISTA survey telescope in Chile, the team found a peanut-shaped bulge with an elongated bar and a prominent X-structure, which had been hinted at in previous studies. This indicates that the Milky Way was originally a pure disk of stars, which then formed a thin bar, before buckling into the boxy peanut shape seen today.

The scientists expect that this measurement of the three-dimensional density of the bulge will help to constrain galaxy evolution models for both our Milky Way and spiral galaxies in general. It will also support a number of further studies on different stellar populations, gas flows, or microlensing.

Read the MPE press release and the ESO press release for more images and a movie simulation of the bulge rotating. The research is published as “Mapping the three-dimensional density of the Galactic bulge with VVV red clump stars” by C. Wegg et al. in the Monthly Notices of the Royal Astronomical Society.

Astronomers have used data from the Spitzer Space Telescope to measure the distances, and hence temperatures, of so-called “brown dwarfs” (see Section 9.5).

These brown dwarfs, the coldest known free-floating celestial bodies, were found to be warmer than previously thought, with surface temperatures ranging from about 250 to 350 degrees Fahrenheit (125 to 175 degrees Celsius). By comparison, the Sun has a surface temperature of about 10,000 degrees Fahrenheit (around 6000 degrees Celsius).

To reach these surface temperatures after cooling for billions of years, these objects would have to have masses of only 5 to 20 times that of Jupiter. Unlike the Sun, the only source of energy for these coldest of brown dwarfs is from their gravitational contraction, which depends directly on their mass. The Sun is powered by the conversion of hydrogen to helium; these brown dwarfs are not hot enough for this type of “nuclear burning” to occur.


Credit: NASA/JPL-Caltech

The findings help researchers understand how planets and stars form, but also present new puzzles to astronomers who study cool, planet-like atmospheres, as the observable properties don’t correlate with temperature in a straight-forward way. Ongoing studies of newly discovered brown dwarfs may shed some light (and heat) on these outstanding issues.

Read the JPL press release for more detail and additional images.