Dozens of
rocky bodies that are part of a sea of small rocky fragments never observed
before have been spotted in the suburbs of our solar system beyond planet
Neptune, thanks to a novel technique.
These newly
detected chunks of dust and rock coined Trans-Neptunian Objects (TNO) are smaller
than 330 feet (100 meters) across. They are leftovers from the formation
of planets.
Scientists
had previously detected TNOs larger than 31 miles (50 kilometer) across such as
the Kuiper Belt Objects (KBO), a subset of TNOs. They suspected that there may
be distant objects beyond Neptune since the 1940's, but it wasn't until 1992
that the first KBO was discovered.
Since then,
they've found so many large objects in the outskirts of the solar system that
they had to come up with crazy names,
like Plutinos, Centaurs, and Cubewanos, to keep them in order. And although
researchers suspected the presence of smaller objects, they didn't have a way
to detect the sea of debris.
"The
searches for Kuiper Belt Objects usually look for reflected light from the Sun
and the small motion relative to fixed background stars," said Asantha
Cooray, assistant professor of Physics and Astronomy at the University of
California, Irvine. The amount of reflected light from a small body, however,
is so extremely dim that not even the largest telescopes, or much larger
telescopes one could imagine building either on Earth or space, could see it.
But scientists didn't look
for the reflected light this time. Examining data from NASA's Rossi X-ray Timing Explorer, they
monitored the light from a background star,
Scorpius X-1, as small objects moved in front of it in what are called
occultations. They found obvious dips in the light.
Other than
the Sun, Scorpius X-1 is the brightest
X-ray source in the sky, said study leader Hsiang-Kuang Chang, Associate
Professor of Physics & Institute of Astronomy at the National Tsing Hua
University, Taiwan.
"We
discussed various possibilities for causing these dips and concluded that
occultation by small TNOs are the most likely one," he told SPACE.com
in an email interview.
Alltogether,
Chang and colleagues identified 58 definite dips. Their findings are detailed
in the Aug. 10 issue of the journal Nature.
Observing
occultations is a widely known method for studying foreground objects by
monitoring the light of background stars. The rings of Uranus were first
discovered during an occultation of a star by Uranus. But never have such small
objects been detected this way.
"The
interesting thing here is that instead of monitoring optical stars, these
authors monitor light from an X-ray source since X-ray detectors can record
light at small time intervals compared to optical detectors," Cooray told SPACE.com.
"A 100-meter body only occults a background source for about 10
milliseconds and optical detectors cannot record light continuously at such
small time intervals."
Based on
this finding, the researchers estimate that the number of TNOs reaches around a
quadrillion, rather than the mere billions to a trillion as previously thought.
This shows
an extremely dense disk of material at the outer edges of the solar system
mostly populated by smaller bodies, Cooray said. "Since these are leftover
material from the solar system formation process, it says that the original
disk from which the planets formed was more massive at distances around Neptune
than previously suggested and in strong conflict with some of the early models
for the formation of Kuiper Belt Objects."
advertisement
