from the just-taking-a-stroll-through-the-neighborhood dept.
Astronomers are still hoping for another mission to Pluto, or perhaps another Kuiper belt object:
A grassroots movement seeks to build momentum for a second NASA mission to the outer solar system, a generation after a similar effort helped give rise to the first one. That first mission, of course, was New Horizons, which in July 2015 performed the first-ever flyby of Pluto and is currently cruising toward a January 2019 close encounter with a small object known as 2014 MU69.
[...] Nearly three dozen scientists have drafted letters in support of a potential return mission to Pluto or to another destination in the Kuiper Belt, the ring of icy bodies beyond Neptune's orbit, Singer told Space.com. These letters have been sent to NASA planetary science chief Jim Green, as well as to the chairs of several committees that advise the agency, she added. "We need the community to realize that people are interested," Singer said. "We need the community to realize that there are important, unmet goals. And we need the community to realize that this should have a spot somewhere in the Decadal Survey." That would be the Planetary Science Decadal Survey, a report published by the National Academy of Sciences that lays out the nation's top exploration priorities for the coming decade.
New Horizons 2 was already cancelled due to a shortage of plutonium-238, which still reportedly persists. One proposed target was 47171 Lempo, a trinary system. The trans-Neptunian dwarf planets Eris, Haumea, Sedna, Orcus, Salacia, Makemake, and 2007 OR10 (the largest known body in the solar system without a name - with an estimated 1,535 km diameter) have all been discovered since 2002. Several of these TNOs have moons and Haumea was recently found to have a ring system.
Now that Cassini is dead, most new NASA missions are focused on Mars and Jupiter, leaving the solar system's "ice giants" relatively unstudied:
With instrumentation ever-improving, there were two more worlds waiting for their post-Voyager close ups. It's a promise that has been painfully unfulfilled. Uranus and Neptune, it turns out, are typical of some of the most common planets in our galaxy. Understanding them would not only help us understand the Solar System, its origins, and the interactions that define the outer border of its planets. It would help us make sense of the galaxy as a whole.
Plus those planets have a collection of moons that has the potential to include Enceladus-level surprises. And Uranus is tilted on its side—its axis of rotation is more or less on the plane of the Solar System, rather than pointing perpendicular to it. And its magnetic field is 60º off that axis. It's hard to imagine there's not some amazing stuff to learn there.
The Ice Giants Pre-Decadal Study group has indicated that only one mission would likely be sent to either Uranus or Neptune in the coming decades, due to costs and the need for plutonium-238. The authors concluded that both Uranus and Neptune are of equal importance, but seem to favor going to Uranus first.
Previously: Return to Pluto? - "Scientists, including New Horizons principal investigator Alan Stern, met in Houston on April 24th to discuss the possibility of a Pluto orbiter mission..."
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Scientists, including New Horizons principal investigator Alan Stern, met in Houston on April 24th to discuss the possibility of a Pluto orbiter mission. The mission would likely cost $1-2 billion, compared to around $700 million for New Horizons and $467 million for the Dawn mission to Vesta and Ceres. A launch date in the late 2020s is possible, with a 2030 launch coinciding with the 100th anniversary of Pluto's discovery:
[A] Pluto orbiter mission is a long way from becoming reality, Stern stressed. He said he and his fellow researchers aim to mature the concept in time for it to be considered during the next Planetary Science Decadal Survey, a U.S. National Research Council effort that sets exploration priorities for NASA every 10 years. The next decadal survey will start in 2020, finish in 2022 and be published in 2023, Stern said.
Using the Space Launch System (SLS) could reduce travel time compared to the nine-and-half-year journey of New Horizons, but braking would be required to orbit the Pluto-Charon system, increasing the total travel time back to around seven to nine years. Other missions being considered include flybys of more distant Kuiper Belt dwarf planets (Eris, Sedna, etc.) and exploration of Neptune's moons Triton and Nereid, which are likely captured Kuiper Belt Objects. Triton has about a 14% larger radius and 64% more mass than Pluto. Voyager 2 observed 40% of Triton's surface in 1989.
The Ice Giants Pre-Decadal Study group has proposed sending a mission to either Uranus or Neptune. Only one mission is likely to be approved due to a shortage of plutonium-238 for the radioisotope thermoelectric generators required for an outer solar system mission:
Uranus and Neptune have never got much attention from us – we've only passed each once and never hung around. But that could change. A NASA group has now outlined possible missions to make it to one of these outer worlds to gather data on their composition. This should teach us about them and similar planets in other solar systems.
"The preferred mission is an orbiter with an atmospheric probe to either Uranus or Neptune – this provides the highest science value, and allows in depth study of all aspects of either planet's system: rings, satellites, atmosphere, magnetosphere," says Amy Simon, co-chair of the Ice Giants Pre-Decadal Study group.
There are four proposed missions – three orbiters and a fly-by of Uranus, which would include a narrow angle camera to draw out details, especially of the ice giant's moons. It would also drop an atmospheric probe to take a dive into Uranus's atmosphere to measure the levels of gas and heavy elements there.
The three must-haves for each orbiter mission are a narrow-angle camera, a doppler imager and a magnetometer, while an orbiter containing 15 instruments would add plasma detectors, infrared and UV imaging, dust detection and microwave radar capability. The orbiter could be either a Neptune mission with an atmospheric probe, a Uranus probe of the same design, or a craft sent to a[sic] Uranus that ditches the atmospheric probe for the suite of 15 instruments.
Obligatory grade school humor:
Also at The Verge.
It's not just Saturn and gas giants such as Uranus which have rings in our solar system – as a tiny dwarf planet has just been spotted with its very own.
It's the first dwarf planet beyond Neptune to be spotted with its own ring – and could prove that such rings are not uncommon in the outer solar system.
takyon: Haumea has two known moons as well as this newly discovered ring:
A stellar occultation observed on 21 January 2017 indicated the possibility of a ring system around Haumea. As published in Nature on 11 October 2017, this occultation was confirmed to be a ring, representing the first such ring discovered for a TNO. The ring has a radius of about 2,287 km, a width of ~70 km and an opacity of 0.5. The ring plane coincides with Haumea's equator and the orbit of its larger, outer moon Hi'iaka. The ring is close to the 3:1 resonance with Haumea's rotation.
Haumea is known for its extremely elongated shape, a consequence of its rapid rotation.
The size, shape, density and ring of the dwarf planet Haumea from a stellar occultation (DOI: 10.1038/nature24051) (DX)
A Government Accountability Office report has found that the U.S. is unlikely to produce enough Plutonium-238 for NASA missions about a decade from now. The isotope has been used in radioisotope thermoelectric generators (RTGs) on missions such as Voyager, Cassini, and the Mars Science Laboratory:
Another GAO report notes: "[...], DOE currently maintains about 35 kilograms (kg) [77 pounds] of Pu-238 isotope designated for NASA missions, about half of which meets power specifications for spaceflight. However, given NASA's current plans for solar system exploration, this supply could be exhausted within the next decade."
[...] To address the plutonium problem, in 2011 NASA provided funding to the Department of Energy (DOE) to restart domestic production of the substance. The program is called the Pu-238 Supply Project. So far, the Project has produced ∼3.5 ounces (100 grams) of Pu-238. DOE identified an interim goal of producing 10 to 17.5 ounces (300 to 500 grams) of new Pu-238 per year by 2019. The goal is to produce 1.5 kilograms of new Pu-238 per year—considered full production—by 2023, at the earliest.
GAO is questioning the Supply Project's ability to meet its goal of producing 1.5 kilograms of new Pu-238 per year by 2026. For one thing, the oversight agency's interviews with DOE officials revealed that the agency hasn't perfected the chemical processing required to extract new Pu-238 from irradiated targets to meet production goals.
Only one DOE reactor is currently qualified to make Pu-238:
NASA's plutonium will be produced at two of these reactors, but only one of them is currently qualified to make Pu-238. GAO reported that initial samples of the new Pu-238 did not meet spaceflight specifications because of impurities. However, according to DOE, the samples can be blended and used with existing Pu-238.