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Tag: Uranus

  • The End Is Near for NASA’s Voyager Probes

    The End Is Near for NASA’s Voyager Probes

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    Saturn as captured by the Voyager program.

    Smith Collection/Gado/Getty Images

    Once the Voyagers’ planetary journeys were over, it was possible to begin a new mission phase. After their last planetary stops, both probes reached escape velocity for the solar system, allowing them to be released from the sun’s gravity. Since 2012 for Voyager 1, and 2018 for Voyager 2, they have become interstellar. We know this because after those dates, sensors on the probes showed that charged particles from the sun became less numerous and energetic than those detected from the galactic environment. This was a golden opportunity to study the boundaries of the solar system and the environment outside of it.

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    The Voyager 1 and 2 spacecraft carried Golden Records—recordings of sounds and images intended to show extraterrestrial beings the life and culture of Earth.

    Space Frontiers/Getty Images

    The Secret to a Long Life

    Reaching such a distance is only possible with the right energy source. Many probes use solar panels, but if they move too far from the sun, they become useless (the farthest probe that uses them is the Juno probe orbiting Jupiter). The secret of the Voyagers lies in their atomic hearts: both are equipped with three radioisotope thermoelectric generators, or RTGs—small power generators that can produce power directly on board. Each RTG contains 24 plutonium-238 oxide spheres with a total mass of 4.5 kilograms.

    Plutonium-238 is an unstable isotope, which means it undergoes radioactive decay. The plutonium atoms in the RTGs release alpha particles—comprising two protons and two neutrons—and these hit the RTG canister, heating it up. The heat is then converted into electricity.

    An RTG built for the Voyager program.

    An RTG built for the Voyager program.

    NASA/JPL/Voyager

    But as time passes, the plutonium on board is depleted, and so the RTGs produce less and less energy. The Voyagers are therefore slowly dying. Nuclear batteries have a maximum lifespan of 60 years.

    In order to conserve the probes’ remaining energy, the mission team is gradually shutting down the various instruments on the probes that are still active. For example, in October, Voyager 2’s plasma science instrument—which measures electrically charged atoms passing the probe—was turned off; the same device on Voyager 1 was turned off in 2007 due to a malfunction. These instruments were used to study charged particles in the sun’s magnetic field, and it is precisely this detector in 2018 that determined that Voyager 2 had exited the heliosphere and become interstellar.

    Four active instruments remain, including a magnetometer as well as other instruments used to study the galactic environment, with its cosmic rays and interstellar magnetic field. But these are in their last years. In the next decade—it’s hard to say exactly when—the batteries of both probes will be drained forever.

    This story originally appeared on WIRED Italia and has been translated from Italian.

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  • Tiny new moons have been spotted orbiting Neptune and Uranus

    Tiny new moons have been spotted orbiting Neptune and Uranus

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    The planets Uranus (left) and Neptune (right) have a few additional moons

    NASA, ESA, Mark Showalter (SETI Institute), Amy Simon (NASA-GSFC), Andrew I. Hsu, Michael H. Wong (UC Berkeley)

    Astronomers have spotted new moons around Uranus and Neptune for the first time in a decade. These are the faintest moons ever spotted orbiting any planet, and they prove a long-standing idea about satellites in the outer solar system.

    Scott Sheppard at the Carnegie Institution for Science in Washington DC and his colleagues found these moons using the Magellan telescope in Chile and confirmed them using several other large telescopes around the world. “We looked about four times deeper than anyone has before,” says Sheppard. “These moons are on the edge of our ability – they’re just faint, faint points of light.”

    Generally, when looking for moons, you can only take a picture with a maximum exposure of about 5 minutes before the image becomes overexposed and the movement of the moons makes it useless. Sheppard and his team got around this by taking many of these 5-minute images in a row, observing for hours and then combining the dim parts of the images. That enabled them to spot the dim points of light shining from the faintest moons ever discovered – and the smallest moons found to date around their respective planets.

    The new moon around Uranus is provisionally named S/2023 U1, but it will eventually be given the name of a character in a Shakespeare play, to match the planet’s other moons. It is only about 8 kilometres across, and it completes an orbit once every 680 Earth days.

    One of the new moons around Neptune is called S/2021 N1, and it awaits an official name from Greek mythology. It is about 14 kilometres across and takes about 27 Earth years to orbit the planet, making it the most distant moon from its host planet ever found. It is also the faintest moon ever found.

    The discovery image of the new Uranian moon S/2023 U1, with scattered light from Uranus and trails from background stars

    Scott S. Sheppard/Carnegie Institution for Science

    The brighter, larger moon found orbiting Neptune is called S/2002 N5 – as its name suggests, it was first spotted more than 20 years ago, but it was lost before astronomers could confirm its orbit. “You can lose a moon really easily,” says Sheppard. “We basically need really, really good weather, we need the telescope to be working perfectly, we need everything to go right to detect these moons.” If anything goes wrong and a night of planned observations is lost, moons move in their orbits and become extremely difficult to find again, as happened with S/2002 N5.

    Each of the three new moons has a similar orbit to two other satellites in its planetary system, and these fellow travellers form small groups that orbit together. This means that each of these groups probably formed together when a larger moon broke up in the chaos of the early solar system.

    “Until now it was unclear whether Uranus and Neptune had these groups of outer moons like Jupiter and Saturn do,” says Sheppard. “We believe these are fragments of once bigger moons, and there are probably many more smaller ones to find.” Unfortunately, we are at the limits of what we can discover with current technology, he says, so it might be another long wait before any smaller moons than these are spotted around Uranus and Neptune.

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