Category Archives: Space Science

Asteroids & Comets, Astronomy, Space Science

Hubble: Interstellar visitor ‘Oumuamua leaving faster than expected

The interstellar object that passed through the solar system continues to provide surprises:

Hubble sees `Oumuamua getting a boost 
New results indicate interstellar nomad is a comet 

`Oumuamua, the first interstellar object discovered in the Solar System, is moving away from the Sun faster than expected. This anomalous behaviour was detected using the NASA/ESA Hubble Space Telescope in cooperation with ground-based telescopes. The new results suggest that `Oumuamua is most likely a comet and not an asteroid. The discovery appears in the journal Nature.

This diagram shows the orbit of the interstellar object ‘Oumuamua as it passes through the Solar System. It shows the predicted path of ‘Oumuamua and the new course, taking the new measured velocity of the object into account. ‘Oumuamua passed the distance of Jupiter’s orbit in early May 2018 and will pass Saturn’s orbit January 2019. It will reach a distance corresponding to Uranus’ orbit in August 2020 and of Neptune in late June 2024. In late 2025 ‘Oumuamua will reach the outer edge of the Kuiper Belt, and then the heliopause — the edge of the Solar System — in November 2038.

`Oumuamua — the first interstellar object discovered within our Solar System — has been the subject of intense scrutiny since its discovery in October 2017 [1]. Now, by combining data from the NASA/ESA Hubble Space Telescope, the Canada-France-Hawaii Telescope, ESO’s Very Large Telescope and the Gemini South Telescope, an international team of astronomers has found that the object is moving faster than predicted. The measured gain in speed is tiny and `Oumuamua is still slowing down because of the pull of the Sun — just not as fast as predicted by celestial mechanics.

The team, led by Marco Micheli (European Space Agency) explored several scenarios to explain the faster-than-predicted speed of this peculiar interstellar visitor. The most likely explanation is that `Oumuamua is venting material from its surface due to solar heating — a behaviour known as outgassing [2]. The thrust from this ejected material is thought to provide the small but steady push that is sending `Oumuamua hurtling out of the Solar System faster than expected — as of 1 June, it is travelling with about 114 000 kilometres per hour.

Such outgassing is a typical behaviour for comets and contradicts the previous classification of `Oumuamua as an interstellar asteroid.

“We think this is a tiny, weird comet,” comments Marco Micheli. “We can see in the data that its boost is getting smaller the farther away it travels from the Sun, which is typical for comets.”

Usually, when comets are warmed by the Sun they eject dust and gas, which form a cloud of material — called a coma — around them, as well as the characteristic tail. However, the research team could not detect any visual evidence of outgassing.

“We did not see any dust, coma, or tail, which is unusual,” explains co-author Karen Meech (University of Hawaii, USA) who led the discovery team’s characterisation of `Oumuamua in 2017. “We think  that ‘Oumuamua may vent unusually large, coarse dust grains.”

The team speculated that perhaps the small dust grains adorning the surface of most comets eroded during `Oumuamua’s journey through interstellar space, with only larger dust grains remaining. A cloud of these larger particles would not be bright enough to be detected by Hubble.

Not only is `Oumuamua’s hypothesised outgassing an unsolved mystery, but also its interstellar origin. The team originally performed the new observations on `Oumuamua to exactly determine its path which would have probably allowed it to trace the object back to its parent star system. The new results means it will be more challenging to obtain this information.

“The true nature of this enigmatic interstellar nomad may remain a mystery,” concludes team member Olivier Hainaut (European Southern Observatory, Germany). “`Oumuamua’s recently-detected gain in speed makes it more difficult to be able to trace the path it took from its extrasolar home star.”

This artist’s impression shows the first interstellar object discovered in the Solar System, `Oumuamua. Observations made with the NASA/ESA Hubble Space Telescope and others show that the object is moving faster than predicted while leaving the Solar System. Researchers assume that venting material from its surface due to solar heating is responsible for this behaviour. This outgassing can be seen in this artist’s impression as a subtle cloud being ejected from the side of the object facing the Sun. As outgassing is a behaviour typical for comets, the team thinks that `Oumuamua’s previous classification as an interstellar asteroid has to be corrected. [Higher res images]
Notes

[1]`Oumuamua, pronounced “oh-MOO-ah-MOO-ah”, was first discovered using the Pan-STARRS telescope at the Haleakala Observatory, Hawaii. Its name means “a messenger from afar, arriving first” in Hawaiian, and reflects its nature as the first known object of interstellar origin to have entered the Solar System.

[2] The team tested several hypotheses to explain the unexpected change in speed. They analysed whether solar radiation pressure, the Yarkovsky effect, or friction-like effects could explain the observations. It was also checked whether the gain in speed could have been caused by an impulse event (such as a collision), by `Oumuamua being a binary object or by `Oumuamua being a magnetised object. Also, the unlikely theory that `Oumuamua is an interstellar spaceship was rejected: the smooth and continuous change in speed is not typical for thrusters and the object is tumbling on all three axes, speaking against it being an artificial object.

Asteroids & Comets, Space Science

NASA DART and ESA Hera to study deflecting asteroids via spacecraft impact

ESA and NASA are testing defenses against an asteroid threat:

Earth’s first mission to a binary asteroid,
for planetary defence

Hera is the European contribution to an ESA-NASA double-spacecraft mission intended to test whether a kinetic deflection technique can be used to shift the orbit of an asteroid. Target of the mission is a double asteroid system, called Didymos, which will come a comparatively close 11 million km to Earth in 2022. The 800-m diameter main body is orbited by a 170-m moon, informally called ‘Didymoon’. In 2022 NASA will first perform a kinetic impact on the smaller of the two bodies, then Hera will follow-up with a detailed post-impact survey that will turn this grand-scale experiment into a well-understood and repeatable planetary defence technique.

25 June 2018: Planning for humankind’s first mission to a binary asteroid system has entered its next engineering phase. ESA’s proposed Hera mission would also be Europe’s contribution to an ambitious planetary defence experiment.

Named for the Greek goddess of marriage, Hera would fly to the Didymos pair of Near-Earth asteroids: the 780 m-diameter mountain-sized main body is orbited by a 160 m moon, informally called ‘Didymoon’, about the same size as the Great Pyramid of Giza.

“Such a binary asteroid system is the perfect testbed for a planetary defence experiment but is also an entirely new environment for asteroid investigations. Although binaries make up 15% of all known asteroids, they have never been explored before, and we anticipate many surprises,”

explains Hera manager Ian Carnelli.

“The extremely low-gravity environment also presents new challenges to the guidance and navigation systems. Fortunately we can count on the unique experience of ESA’s Rosetta operations team which is an incredible asset for the Hera mission.”

The smaller Didymoon is Hera’s main focus: the spacecraft would perform high-resolution visual, laser and radio science mapping of the moon, which will be the smallest asteroid visited so far, to build detailed maps of its surface and interior structure.

By the time Hera reaches Didymos, in 2026, Didymoon will have achieved historic significance: the first object in the Solar System to have its orbit shifted by human effort in a measurable way.

A NASA mission called the Double Asteroid Redirection Test, or DART, is due to collide with it in October 2022. The impact will lead to a change in the duration of Didymoon’s orbit around the main body. Ground observatories all around the world will view the collision, but from a minimum distance of 11 million km away.

“Essential information will be missing following the DART impact – which is where Hera comes in,” adds Ian. “Hera’s close-up survey will give us the mass of Didymoon, the shape of the crater, as well as physical and dynamical properties of Didymoon.

“This key data gathered by Hera will turn a grand but one-off experiment into a well-understood planetary defence technique: one that could in principle be repeated if we ever need to stop an incoming asteroid.”

The traditional method of estimating the mass of a planetary body is to measure its gravitational pull on a spacecraft. That is not workable within the Didymos system: Didymoon’s gravitational field would be swamped by that of its larger partner.

Hera uses infrared to scan impact crater.

Instead, Hera imagery will be used to track key landmarks on the surface on the bigger body, ‘Didymain’, such as boulders or craters. By measuring the ‘wobble’ Didymoon causes its parent, relative to the common centre of gravity of the overall two-body system, its mass could be determined with an accuracy over 90%.

Hera will also measure the crater left by DART to a resolution of 10 cm, accomplished through a series of daring flybys, giving insight into the surface characteristics and internal composition of the asteroid.

“Hera benefits from more than five years of work put into ESA’s former Asteroid Impact Mission,” comments Ian. “Its main instrument is a replica of an asteroid imager already flying in space – the Framing Camera used by NASA’s Dawn mission as it surveys Ceres, which is provided by the German Aerospace Center, DLR.

“It would also carry a ‘laser radar’ lidar for surface ranging, as well as a hyperspectral imager to characterise surface properties. In addition, Hera will deploy Europe’s first deep space CubeSats to gather additional science as well as test advanced multi-spacecraft intersatellite links.”

NASA’s DART mission meanwhile has passed its preliminary design review and is about to enter its ‘Phase C’ detailed design stage.

In 2022, NASA’s Double Asteroid Redirection Test (DART) collides with the smaller body of the Didymos binary asteroid system in an attempt to measurably shift its orbit. ESA’s Hera mission, now under study, will examine the aftermath of this impact to help determine whether humans can deflect threatening asteroids.

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Mars, Space Science

A blue sand dune on Mars

Mars has lots of weird and wonderful features on its surface. For example, here is one highlighted by NASA last week:

Once in a Blue Dune

Sand dunes often accumulate in the floors of craters. In this region of Lyot Crater, NASA’s Mars Reconnaissance Orbiter (MRO) shows a field of classic barchan dunes on Jan. 24, 2018.

Just to the south of the group of barchan dunes is one large dune with a more complex structure. This particular dune, appearing like turquoise blue in enhanced color, is made of finer material and/or has a different composition than the surrounding.

The map is projected above at a scale of 25 centimeters (9.8 inches) per pixel. [The original image scale is 34.7 centimeters (13.7 inches) per pixel (with 1 x 1 binning); objects on the order of 104 centimeters (40.9 inches) across are resolved.] North is up.

This is a stereo pair with ESP_053406_2295.

The University of Arizona, Tucson, operates HiRISE, which was built by Ball Aerospace & Technologies Corp., Boulder, Colorado. NASA’s Jet Propulsion Laboratory, a division of Caltech in Pasadena, California, manages the Mars Reconnaissance Orbiter Project for NASA’s Science Mission Directorate, Washington.

Image Credit: NASA/JPL-Caltech/Univ. of Arizon

Image download options

Mars, Space Science

Curiosity rover images the Martian haze during global dust storm

The dust storm on Mars that had has cut off the Opportunity rover’s access to the power of the Sun has now engulfed the whole planet:

Martian Dust Storm Grows Global
Curiosity Captures Photos of Thickening Haze 

A storm of tiny dust particles has engulfed much of Mars over the last two weeks and prompted NASA’s Opportunity rover to suspend science operations. But across the planet, NASA’s Curiosity rover, which has been studying Martian soil at Gale Crater, is expected to remain largely unaffected by the dust. While Opportunity is powered by sunlight, which is blotted out by dust at its current location, Curiosity has a nuclear-powered battery that runs day and night.

A self-portrait taken by NASA’s Curiosity rover taken on Sol 2082 (June 15, 2018). A Martian dust storm has reduced sunlight and visibility at the rover’s location in Gale Crater. Image Credit: NASA/JPL-Caltech/MSSS > Larger view

The Martian dust storm has grown in size and is now officially a “planet-encircling” (or “global”) dust event.

Though Curiosity is on the other side of Mars from Opportunity, dust has steadily increased over it, more than doubling over the weekend. The sunlight-blocking haze, called “tau,” is now above 8.0 at Gale Crater — the highest tau the mission has ever recorded. Tau was last measured near 11 over Opportunity, thick enough that accurate measurements are no longer possible for Mars’ oldest active rover.

For NASA’s human scientists watching from the ground, Curiosity offers an unprecedented window to answer some questions. One of the biggest is: why do some Martian dust storms last for months and grow massive, while others stay small and last only a week?

“We don’t have any good idea,”

says Scott D. Guzewich, an atmospheric scientist at NASA Goddard Space Flight Center in Greenbelt, Maryland, leading Curiosity’s dust storm investigation.

Curiosity, he points out, plus a fleet of spacecraft in the orbit of Mars, will allow scientists for the first time to collect a wealth of dust information both from the surface and from space. The last storm of global magnitude that enveloped Mars was in 2007, five years before Curiosity landed there.

Two images from the Mast Camera (Mastcam) on NASA’s Curiosity rover depicting the change in the color of light illuminating the Martian surface since a dust storm engulfed Gale Crater. The left image shows the “Duluth” drill site on Sol 2058 (May 21); the right image is from Sol 2084 (June 17). The cherry red color is largely due to red dust grains in the atmosphere letting red light through to the surface, but not green or blue light. Image Credit: NASA/JPL-Caltech/MSSS › Larger view

In the animation above, Curiosity is facing the crater rim, about 18.6 miles (30 kilometers) away from where it stands inside the crater. Daily photos captured by its Mast Camera, or Mastcam, show the sky getting hazier. This sun-obstructing wall of haze isabout six to eight times thicker than normal for this time of season.

Curiosity’s engineers at NASA’s Jet Propulsion Laboratory in Pasadena, California, have studied the potential for the growing dust storm to affect the rover’s instruments, and say it poses little risk. The largest impact is to the rover’s cameras, which require extra exposure time due to the low lighting. The rover already routinely points its Mastcam down at the ground after each use to reduce the amount of dust blowing at its optics. JPL leads the Mars Science Laboratory/Curiosity mission.

Martian dust storms are common, especially during southern hemisphere spring and summer, when the planet is closest to the Sun. As the atmosphere warms, winds generated by larger contrasts in surface temperature at different locations mobilize dust particles the size of individual talcum powder grains. Carbon dioxide frozen on the winter polar cap evaporates, thickening the atmosphere and increasing the surface pressure. This enhances the process by helping suspend the dust particles in the air. In some cases, the dust clouds reach up to 40 miles (60 kilometers) or more in elevation.

Though they are common, Martian dust storms typically stay contained to a local area. By contrast, the current storm, if it were happening on Earth, is bigger than North America and Russia combined, says Guzewich.

The dust storm may seem exotic to some Earthlings, but it’s not unique to Mars. Earth has dust storms, too, in desert regions such as NorthAfrica, the Middle East, and the southwest United States.

But conditions here prevent them from spreading globally, said Ralph A. Kahn, a Goddard senior research scientist who studies the atmospheres of Earth and Mars. These include the structure of our thicker atmosphere and stronger gravity that helps settle dust. Earth also has vegetation cover on land that binds the soil with its roots and helps block the wind and rain that wash the particles out of the atmosphere.

In June 2018 NASA’s Curiosity Rover used its Mast Camera, or Mastcam, to snap photos of the intensifying haziness the surface of Mars, caused by a massive dust storm. The rover is standing inside Gale Crater looking out to the crater rim. The photos span about a couple of weeks, starting with a shot of the area before the storm appeared. > Larger image

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Update on Opportunity: Opportunity Hunkers Down During Dust Storm | NASA

 

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Activism, Space Science, Space Systems

Video: PlanetVac tested on Masten Space’s Xodiac rocket

I’ve previously posted about the PlanetVac system for gathering a sample of the surface of celestial bodies. It was developed by Honeybee Robotics and supported financially by the Planetary Society. Here is a video report on a recent test using Masten Space Systems‘s Xodiac vertical takeoff and landing reusable rocket.

From the caption:

Taking samples of other worlds is an important step towards discovery, but it is an expensive and complex process. Honeybee Robotics and The Planetary Society
teamed up to solve this problem. This is PlanetVac.

Learn more: http://www.planetary.org/planetvac/

After a few prototypes, PlanetVac is ready to be tested in Mojave, CA on a Xodiac rocket made by Masten Space Systems. NASA selected PlanetVac to fly on a Xodiac rocket as part of its Flight Opportunities program. If this PlanetVac Xodiac test is successful, it will significantly increase its chance of being selected on a real space mission.

PlanetVac Xodiac was supported by Planetary Society members. Over 800 people joined the team by donating. Thank you to the 887 donors from 35 countries who supported PlanetVac Xodiac in 2018. Special thanks to Pendleton Ward and Dustin Roberts who provided generous matching funds to inspire the community in support of the project.

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