Space Sunday: looking back on Earth and landing rockets and probes

The Earth and Moon, as seen from orbit over Mars, November 20th 2016
The Earth and Moon, as seen from orbit over Mars, November 20th 2016

Two marbles sit on a midnight background, one a swirl of blue, white, brown and green, the other tinted in shades of grey. Together they are the Earth and her Moon as seen by the most powerful imagining system currently orbiting the planet Mars.

It is, in fact a composite image, although Earth and the Moon are the correct sizes and the correct position / distance relative to one another. The images were captured by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA’s Mars Reconnaissance Orbiter (MRO) on November 26th, 2016.

The images were taken to calibrate HiRISE data, since the reflectance of the moon’s Earth-facing side is well-known. As such, this is not the first image of our home planet and its natural satellite captured from Martian orbit, but it is one of the most striking. Whilst a composite image, only the Moon’s brightness has been altered to enhance its visibility; were it to be shown at the same brightness scale as Earth, it would barely be visible. That it appears to be unnaturally close to Earth is in fact an illusion of perspective: at the time the pictures were taken, the Moon was on the far side of Earth relative to Mars, and about to pass behind it.

The image of Earth shows Australia prominent in the central area of the image, its shape just discernible in this high-resolution image, taken when Mars and the MRO were 205 million kilometres (147 million miles) from Earth.

For me, this is another picture demonstrating just how small, fragile and unique our home world actually is.

 Falcon 9 Makes Triumphant Return to Flight

With Federal Aviation Authority (FAA) approval given, SpaceX, the private space company founded by Elon Musk, made a triumphant return to flight status with its Falcon 9 launch system on Saturday, January 14th.

January 14th, 2017: the SpaceX Falcon 9, carry 10 advanced Iridium Next communications satellites in its bulbous paylod fairing, lifts-off from Space Launch Complex 4E, Vandenberg Air Force Base, California Credit: SpaceX
January 14th, 2017: the SpaceX Falcon 9, carry 10 advanced Iridium NEXT communications satellites in its bulbous payload fairing, lifts-off from Space Launch Complex 4E, Vandenberg Air Force Base, California Credit: SpaceX

SpaceX launches had been suspended in September 2016, after a Falcon 9 and its US $200 million payload were loss in an explosion during what should have been a routine test just two days ahead of the planned launch (see here for more). Towards the end of 2016, and following extensive joint investigations involving NASA and the US Air Force (The Falcon 9 was located at Launch Complex 40 at the Canaveral Air Force Station when the explosion occurred), SpaceX were confident they had traced the root cause for the loss to a failure of process, rather than a structural or other failure within the vehicle itself. However, they had to wait until the FAA had reviewed the investigation findings and approved the Falcon 9’s return to flight readiness before they could resume operations.

The January 14th launch came via the SpaceX West Coast facilities, again leased from the US Air Force, and saw a Falcon 9 booster lift-off from Space Launch Complex 4E at Vandenberg Air Force Base in California. The rocket was carrying the first ten out of at least 70 advanced Iridium NEXT mobile voice and data relay satellites SpaceX will launch over the coming months, as Iridium Communications place a “constellation” of 81 of the satellites in orbit around the Earth in a US $3 billion project.

All ten satellites were successfully lifted to orbit and deployed following a pitch-perfect launch, which had to take place at precisely 9:54:34 local time (17:54:34 UT) in order for all ten satellites to be correctly deployed to reach their assigned orbits. However, all eyes were on the Falcon 9’s first stage, which was set to make a return to Earth for an at-sea landing aboard one of the company’s two autonomous drone landing barges, Just Follow The Instructions.

Down and safe: the Falcon 9 first stage, seen via a camera aboard the autonomous drone barge Just Follow The Instructions, shortly after touch-down on January 14th, 2017. Credit: SpaceX
Down and safe: the Falcon 9 first stage, seen via a camera aboard the autonomous drone barge Just Follow The Instructions, shortly after touch-down on January 14th, 2017. Credit: SpaceX

Operating the Falcon 9 on a basis of reusability is core to SpaceX’s future plans to reduce the overall cost of space launches. While the company has previously made six successful returns and landings with the Falcon 9 first stage, this being the first attempt since September 2016’s loss added further pressure on the attempt. but in the event, it went flawlessly.

After separation from the upper stage carrying the payload to orbit, the first stage of the Falcon 9 completed what are called “burn back” manoeuvres designed to drop it back into the denser atmosphere. Vanes on the rocket’s side were deployed to provide it with stability so that it dropped vertically back down to Earth, using its engines as a braking system and deploying landing legs shortly before touchdown – and the entire journey was captured on video, courtesy of camera built-into the rocket’s fuselage.

Recalling Huygens 12 Years On

I’ve written about NASA’s Cassini mission to Saturn and its moons a few times of late, as September 2017 will see its 20-year mission come to an end. However, I’m returning to it again, as January 14th marked the 12th anniversary of the European  Huygens lander landing on Saturn’s moon Titan.

Named for the Dutch 17th-Century astronomer Christiaan Huygens, who discovered Titan in 1655, the 319 kg (703 lb) 1.3 m (4.3 ft) diameter lander piggybacked a ride to Saturn about the Cassini vehicle in order to attempt a soft landing on whatever lay beneath Titan’s dense atmosphere. Encased in an aeroshell, Huygens detached from Cassini on December 25, 2004, six months after they had reached an initial orbit around Saturn, spinning gently to remain stable as it commenced a long, gentle rendezvous with Titan.

Reaching the moon of January 14th, 2005, the lander entered the huge moon’s atmosphere at roughly 10:15 UTC to commence a 2.5 hours descent to Titan’s surface, most of which was carried out under the canopy of a broad parachute, deployed after the lander had jettisoned its protective aeroshell.

An artist's impression of Huygen's entry, descent and landing on Titan, January 14th, 2005. Credit: ESA
An artist’s impression of Huygen’s entry, descent and landing on Titan, January 14th, 2005. Credit: ESA

The target landing site lay near a region of Titan informally called Xanadu, approximately the size of Australia, and comprising highly reflective water ice. At the time of the decent, researchers had theorised there might be lakes and oceans of liquid hydrocarbons on Titan, so Huygens was designed to float, as well as make a landing on solid ground.

As we now know, the lakes a rivers of Titan are found much closer to the polar regions, so little Huygens eventually touched down on a solid surface. In the process, it became the first vehicle from Earth to land on a body in the outer solar system, and still holds the record for the farthest point from Earth any spacecraft has ever landed.

Huygens enabled studies of the atmosphere and surface, including the first in-situ sampling of the organic chemistry and the aerosols below 150 km (93 mi). These confirmed the presence of a complex organic chemistry, which reinforces the idea that Titan is a promising place to observe the molecules that may have been the precursors of the building blocks of life on Earth.

Titan as seen by Huygens from an altitude of 7 km (4.4 mi) on January 14th, 2005, with the probe still some 20 minutes from touchdown. The curvature evident in the image is an artefact of the image system and distortion due to the atmosphere. Credit: ESA
Titan as seen by Huygens from an altitude of 7 km (4.4 mi) on January 14th, 2005, with the probe still some 20 minutes from touchdown. The curvature evident in the image is an artefact of the image system and distortion due to the atmosphere. Credit: ESA

In addition, and during its descent, the lander provided the first clear images of the surface of Titan from below an altitude of 40 km (25 mi). These revealed an extraordinary, Earth-like place in terms of its meteorology, geomorphology and fluvial activity, just with different ingredients, the images captured showing strong evidence for erosion due to flowing liquid, possibly methane.

The lander touched down with an impact speed similar to dropping a ball on Earth from a height of about 1 metre (3.3 ft), to create a depression 12 cm (4.7 in) deep and kicking up a cloud of dust (most likely organic aerosols)  which remained suspended in the atmosphere for about four seconds after the impact. Instruments showed that the craft bounced a little and slid almost half a metre (18 in) before coming to rest.

The surface of Titan as seen by Huygens. On the left, under local lighting conditions. On the right, under close to Earth normal daylight conditions. Credit: ESA
The surface of Titan as seen by Huygens. On the left, under local lighting conditions. On the right, under close to Earth normal daylight conditions. Credit: ESA

Huygens relayed data from its suite of instruments to Earth via the Cassini orbiter for about 90 minutes, before the latter’s orbit around Saturn carried it out of range. In that time, the lander continued to examine Titan’s atmosphere and sought to determine the nature of Titan’s surface, which is thought to be relatively soft, but covered by a thin crust resembling frozen snow. A communication issue meant that data could only be relayed to Cassini over one of the two planned channels, but to all intents an purposes, Huygens fulfilled its mission before the orbiter passed out of effective communications range, not to return until well after the little lander had exhausted its available power.

In marking the 12th anniversary of the lander’s arrival on Titan, ESA and NASA issued a short video of the mission utilising both animated footage and actual images and video (digitally cleaned-up)  from the probe’s descent through Titan’s atmosphere, as captured by the on-board cameras.

Just How Old is the Moon, and Just How Did It Form?

After starting with the Earth and Moon, I thought I’d close this space Sunday with them.

It’s long been thought that the Moon was formed around 100-200 million years after the primordial Earth, making it about 4.4 billion years old. However, a recent study of the rock samples returned by the Apollo 14 lunar mission are pointing to the Moon actually forming between 4.5 and 4.54 billion years ago, with the most likely age being 4.51 billion years.

This not only makes the Moon older than anticipated, by up to 140 million years (still a blink of the eye in cosmological terms), it also raises questions (again) over how the Moon was actually formed.

The team responsible for the study, from the University of California, Los Angeles (UCLA) have been focusing on fragments of lunar rock which contain a type of silicate mineral called zircon. These fragments were of interest for two reason. The first is that zircon on Earth appeared quite early in the planet’s formation. The second is it contains trace amounts of uranium, thorium, and lutetium, which effectively makes it a highly accurate form of nuclear dating system. By examining the radioactive decay of these elements, and correcting for cosmic ray exposure, the research team was able to get highly precise estimates of the zircon fragments ages, and thus a reasonably accurate estimation of the Moon’s age.

The findings suggest that Earth and Moon formed around the same time, and this lends incidental weight to a separate theory recently put forward by researchers in Israel on how the Moon was formed.

Rather than being the result of a collision between an already formed primordial Earth and a Mars-sized planet (dubber “Theia”) as is commonly proposed, the Israeli team have developed a model which shows that the Moon may have been created as a result of multiple impacts the Earth suffered while it was itself forming. These much smaller collisions threw sufficient material off of our nascent world to create a ring of moonlets, all roughly the same age as the Earth and all composed of the same material.

The traditional theory of the Moon’s formation is that a Mars-sized body grazed the young Earth, throwing of a cloud of material which eventually condensed into the Moon. Credit: NASA
The traditional theory of the Moon’s formation is that a Mars-sized body grazed the young Earth, throwing of a cloud of material which eventually condensed into the Moon. Credit: NASA

Over time, these moonlets naturally collided with one another to form a larger body, which effectively “hoovered up” the rest of the debris from the multiple collisions with Earth, thus giving rise to the Moon as we know it today. What’s significant about the idea, is that it would place the material comprising these moonlets much closer to the Earth’s believed age (around 4.50-4.55 billion years), which pretty much matches the UCLA study – and it explains why the Moon is so geologically similar to the Earth.

The Israeli study doesn’t quite tie-up some of the broad mysteries about our Moon’s formation as postulated by  a team of scientists led by Sarah Stewart, professor of earth and planetary sciences at the University of California  (see this Space Sunday report from November), but it is being seen as a plausible alternate to the “Theia big impact” theory for the Moon’s formation.

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