Day: December 20, 2021

The Parker Solar Probe has finally reached the atmosphere of the Sun.

The NASA spacecraft has spent more than three years winding its way by planets and creeping gradually closer to our star to learn more about the origin of the solar wind, which pushes charged particles across the solar system.

Since solar activity has a large effect on living on Earth, from generating auroras to threatening infrastructure like satellites, scientists want to know more about how the Sun operates to better make predictions about space weather, and gain a better understanding of the mechanisms at work in and around our star. Over the years, we’ve done this with a number of missions – but the most fascinating of all to date is the Parker Solar Probe, a NASA mission that has literally touched the face of the Sun.

The spacecraft – launched in 2018 – is in a complex dance around the Sun that involves skimming closer and closer to our life-giving star, and they sweeping away again, far enough to cross back over the orbit of Venus – indeed, to use Venus as a means to keep itself looping around the Sun in orbits that allow it to gradually get closer and closer, with the aim of actually diving into and out of the Sun’s corona, what we might regard as the Sun’s seething, broiling atmosphere.

In fact, the probe actually first flew through the corona in April 2021; however, it was a few months before the data to confirm this could be returned to Earth, and a few more months to verify it; hence why the news has only just broken about the probe’s success. One of the aims of pushing the probe into the Sun’s corona was to try to locate the a boundary called the Alfvén critical surface. This is the boundary where the solar atmosphere  – held in check by the Sun’s gravity – end, and the solar wind – energetic particles streaming outwards from the Sun with sufficient velocity to break free of that gravity – begins, creating the outwards flow of radiation from our star.

Up until Parker’s April 2021 passage into the corona, scientists has only been able to estimate where Alfvén critical surface lay, putting it at somewhere between 6.9 million and 13.8 million km from the gaseous surface of the Sun. As it passed through the corona, Parker found these estimates to be fairly accurate: the data it returned to Earth put the outer “peaks” of the boundary at 13 million km above the Sun’s surface – or photosphere; the data also revealed the boundary is not uniform; there are “spikes and valleys” (as NASA termed them) where the boundary stretches away from the photosphere at some points, and collapses down much close to it in others. While it has yet to be confirmed, it is theorised this unevenness is the result of the Sun’s 11-year active cycle and various interactions of the atmosphere and solar wind.

The April “dip” into the corona lasted for five hours – as the mission goes on, future “dips” will be for longer periods). But give the spacecraft is travelling at 100 kilometres per second, it was able to gather a lot of data as it zipped around the Sun – and even sample the particles within the corona. The probe’s passage revealed that the corona is dustier than expected, the cause of which has yet to be properly determined, as well as revealing more about the magnetic fields within the corona and how they drive the Sun’s “weather”, generating outbursts like solar flares and coronal mass ejections (CREs), both of which can have considerable impact on life here on Earth.

To survive the ordeal of passing through the corona, where temperatures soar to millions of degrees centigrade, far hotter than those found at the Sun’s photosphere.  – Parker relied on its solar shadow-shield: a hexagonal unit 2.3 m across made of reinforced carbon–carbon composite 11.4 cm thick with an outer face is covered in a white reflective alumina surface layer. This shield is so efficient in absorbing / reflecting heat, whilst passing through the corona the sunward face is heated to around 1,370ºC, but the vehicle, sitting inside the shadow cast by the shield never experiences temperatures higher than 30ºC.

In addition to mapping the Alfvén critical surface, Parker’s April 2021 trip into the Sun’s corona, the probe also passed through a “pseudostreamer,” one of the huge, bright structures that rise above the Sun’s surface and are visible from Earth during solar eclipses. This was compared to flying into the eye of a storm the probe recorder calmer, quieter conditions within the streamer, with few energetic particles within it. Exactly what this means is again unclear at this time, but it does point to further incredibly complex actions and interactions occurring with the Sun.

Since April, Parker has dipped back into the corona twice more, with the November 2021 passage bringing it to around 9.5 million km of the Sun’s photosphere – although again, the data from that pass has yet to be received and analysed. The next passage in February 2022 will again be at roughly the same distance from the photosphere, with a further five passes to follow at the same distance in 2022/23, before a flyby of Venus allows Parker to fly even deeper in to corona. By December 2025, and the mission’s final orbits, it will be descending through the corona to just 6.9 million km from the photosphere.

But that’s not all. Because Parker is in an elliptical around the Sun, it spends a part of its time much further away. This both allows the craft to dissipate absorbed heat from its shield, and for it to observe the Sun from a distance, giving scientists much broader opportunities to study the Sun, such as allowing them to study the physics of “switchbacks”. These are zig-zag-shaped structures in the solar wind, first witness by the joint ESA-NASA Ulysses mission that occupied a polar orbit around the Sun in the 1990s.

In particular, Parker’s observations suggest that rather then being discrete events, switchbacks occur in patches, and that these “patches” of switchbacks are aligned with magnetic funnels coming from the photosphere called called supergranules. These tunnels are thought to be where fast particles of the solar wind originate; so switchbacks may have something of a role to play in the generation of the solar wind or they may be a by-product of its generation or, given they seem to have a higher percentage of helium than other aspects of the solar wind, may serve a highly specialised role as a part of the solar wind.

Right now, scientists are unclear on what might be the case, or what actually generates switchbacks; but gaining clearer insight into their creation, composition and interaction with other particles in the solar wind, and with the Sun’s magnetic field might provide explanations for a number of solar mechanisms, including just why the corona is so much hotter than the photosphere.

Mars 2020 Mission Update

Scientists with NASA’s Mars 2020 Perseverance rover mission have discovered that the bedrock their six-wheeled explorer has been driving on since landing in February likely formed from red-hot magma. It’s a discovery with implications for our understanding and accurately dating critical events in the history of Jezero Crater – as well as the rest of the planet.

Even before the Mars 2020 mission arrived on Mars, there have been much debate about the formation of the rocks in the crater: whether they might be sedimentary in origin, the result compressed accumulation of mineral particles possibly carried to the location by an ancient river system, or whether they might be they igneous, possibly born in lava flows rising to the surface from a now long-extinct Martian volcano. However, whilst studying exposed bedrock at location dubbed “South Séítah” within Jezero, the science team noted a peculiar rock they dubbed “Brac”, selecting it as a location from which to collect further samples of Martian bedrock using the rover’s drill.

When taking samples of this kind, booth Perseverance and her elder sister, Curiosity, operating in Gale Crater half a world away, are both instructed to scour target rocks clean of surface dust and dirt that otherwise might contaminate samples. This is done by using an abrasion tool (think wire brush) mounted alongside the drilling mechanism. However, in checking the work on “Brac”, the mission team realised the abrasion process had revealed the rock was rich in crystalline formations.

Rather than going ahead and drilling the rock for a sample, scientists ordered the rover to study the formations using the Planetary Instrument for X-Ray Lithochemistry (PIXL) instrument  – which is designed to map the elemental composition of rocks. PIXL revealed the formations to be composed of an unusual abundance of large olivine crystals engulfed in pyroxene crystal, indicating the formations grew in slowly cooling magma, offering some confirmation that volcanism has at least be partially involved in Jezero Crater’s history. However, PIXL’s data also suggested the rock, once hardened, has subsequently altered as a result of water action – confirming free-flowing water also had a role to play in the crater’s past..

The crystals within the rock provided the smoking gun … a treasure trove that will allow future scientists to date events in Jezero, better understand the period in which water was more common on its surface, and reveal the early history of the planet. Mars Sample Return is going to have great stuff to choose from.

– Ken Farley, Perseverance Project Scientist

The Sample Return mission has yet to be fully defined, let alone funded, but is being looked at as a mission for the early 2030s, quite possibly with European Space Agency involvement. In the meantime, a question Farley and his colleagues would love to answer is whether the olivine-rich rock formed in a thick lava lake cooling on the surface of Mars, or originated in a subterranean chamber that was later exposed by erosion; knowing the answer to this could determine the early history of Jezero Crater and its surroundings.

This 60-second video pans across an enhanced-color composite image, or mosaic, of the delta at Jezero Crater on Mars. The delta formed billions of years ago from sediment that an ancient river carried to the mouth of the lake that once existed in the crater. Taken by the Mastcam-Z instrument aboard NASA’s Perseverance rover, the video begins looking almost due west of the rover, and sweeps to the right until it faces almost due north.

Also within the latest updates from the Mars 2020 team is the news that Perseverance has found organic compounds within the rocks of Jezero Crater and in the dust that covers them. This discovery was made as a result of a review of findings from the SHERLOC (Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals) instrument.

This does not mean that the rover has discovered evidence of past microbial life on Mars; these carbon compounds can be created by both organic and inorganic processes. However, the fact that they have been found at a number of locations explored by the rover means that the science team can map their spatial distribution, relate them to minerals found in their locations, and thus both further determine their organic / inorganic origins and trace the distribution of minerals, etc., within the crater.

Further, the fact that compounds like these have been identified by both the Curiosity and Perseverance rovers means that potential biosignatures (signs of life, whether past or present) could be preserved, too. IF so, then assuming they exist, there may come a time when one our other rover might happen upon them.

Continue reading “Space Sunday: touching the Sun and Martian organics” →