China prepares for country’s first Mars landing attempt with Tianwen-1

China will attempt to become only the second nation to land a spacecraft on Mars… The post China prepares for country’s first Mars landing attempt with Tianwen-1 appeared first on NASASpaceFlight.com.

China prepares for country’s first Mars landing attempt with Tianwen-1

China will attempt to become only the second nation to land a spacecraft on Mars on Friday, joining the United States. Tianwen-1, China’s first mission to the Red Planet, launched in the middle of last year, sharing the particularly busy July 2020 Martian launch window with NASA’s Mars 2020 mission, including the Perseverance rover and Ingenuity helicopter, and the United Arab Emirates’ Al Amal orbiter.

Within the coming hours, Tianwen-1’s orbiter section is set to jettison it’s lander section, which will attempt to land on Mars’ Utopia Planitia, carrying with it a small rover called Zhurong. Landing is scheduled to occur at 23:11 UTC.

The spacecraft launched from Wenchang Spacecraft Launch Site on the southern Chinese island of Hainan aboard the fifth flight of the country’s Long March 5 heavy lift rocket on 23 July 2020. As well as marking the first time the Long March 5 had launched a payload beyond Earth orbit, the launch of Tianwen-1 also marked China’s first mission to Mars.

Tianwen-1 launching aboard the fifth flight of China’s Long March 5 rocket on July 23 2020 – via CNSA

Despite being the county’s first interplanetary mission, it is rather complex, with the approximately five ton probe consisting of three separate spacecraft, an orbiter, lander and rover.

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  • These three spacecraft launched as one, with the lander/rover section of the spacecraft incapsulated in a small capsule, intended to allow it to pierce through the Martian atmosphere. The three spacecraft have been operating as one in Martian orbit since Tianwen-1 arrived on 10 February.

    The China National Space Administration (CNSA) has been reluctant to share much information of the timeline of the entry, descent and landing procedures, but a rough outline of how Tainwen-1’s landing should play out is known.

    Seven minutes of terror

    Those who have worked on spacecraft that have attempted, successfully or not, to land on the Red Planet, have nicknamed the time in which the spacecraft enters the atmosphere, descends to the surface, and touches down, as the “seven minutes of terror”, mainly because of the complexity of the approximately seven minute journey from the top of the Martian atmosphere to the surface.

    Artist’s impression of the three spacecraft China will send to Mars – via Nature Astronomy/CNSA

    The first order of business for Tianwen-1 will occur approximately five hours prior to landing, when the orbiter, still connected to the capsule containing the lander and rover, will ignite it’s engines to place it in on a trajectory that would see it intersect with the Martian atmosphere. Shortly afterward, the orbiter will separate from the lander/rover capsule, and re-ignite it’s engines to place it back into a safe Martian orbit. This maneuver will place the lander and rover on a course to enter the Martian atmosphere within five hours.

    This descent strategy, temporarily de-orbiting the Tianwen-1 orbiter, avoids the need for the entry capsule to have its own orbital maneuvering system, and is not dissimilar to the strategy used by NASA’s Galileo spacecraft to drop an atmospheric probe into Jupiter in 1995.

    The main entry, descent and landing sequence will begin at around 23:04 UTC, around seven and a half minutes prior to the planned landing time, when the lander and rover are set to hit the Martian atmosphere, travelling at around 4,800 meters per second, protected by a heatshield to keep the two vehicles safe from entry heating.

    Once the spacecraft comes within four kilometers of the Martian surface, the capsule, still encapsulating both the lander and rover, will deploy a parachute to begin slowing the spacecraft as it barrels towards the surface. Shortly afterward, at around 23:06 UTC, the heatshield that had protected the lander during atmospheric entry will be jettisoned and fall to the Martian surface.

    The jettisoning of the heatshield will allow for the lander and rover to separate from the landing capsule and parachute, which is set to occur when the spacecraft is around 1,500 meters above the Martian surface. At around 100 meters above the surface, the lander will ignite its engines and slow down the spacecraft into a hover above Utopia Planitia, allowing it to begin its final descent to the surface.

    Diagram outlining Tianwen-1’s entry, descent and landing sequence – via CNSA

    A suite of cameras and LIDAR (light detecting and ranging) equipment will be used to navigate the spacecraft to touch down.  Assuming this all goes to plan, the lander and rover will touch down on the Martian surface at 23:11 UTC, brining an end to China’s “seven minutes of terror.”

    Surface operations

    Once the lander has touched down in Utopia Planitia, the spacecraft will begin a planned 90 Sols (Martian days) of surface operations, conducting geology, minerology and geophysical investigations, among others.

    The rover, named Zhurong, will be kept on top of the lander, in similar fashion to China’s Chang’e 3 and Chang’e 4 lunar landers, which both carried a small rover atop them during the landing sequence of their missions. To allow for Zhurong to safely make it’s way onto the Martian surface, a ramp will remotely unfold, allowing the rover to drive down to the surface.

    To facilitate its 90 Sol scientific mission, Zhurong is equipped with over six scientific instruments, including a subsurface radar that will allow the rover to peer over 100 meters below the Martian surface, a spectrograph to gain data about the chemical composition of Mar’s surface, and a device provided by the French Institute for Research in Astrophysics and Planetology (IRAP). The device is a calibration target, a duplicate of one IRAP provided NASA’s Curiosity rover. The agency will compare the dataset from the Zhurong calibration target with the dataset from the Curiosity calibration target.

    The landing site, Utopia Planitia, is also very significant in terms of exploration of the Red Planet. On 3 September 1976, NASA’s Viking 2 spacecraft touched down in the region, marking the second ever landing on Mars. Viking 2’s scientific mission lasted nearly four years until its batteries failed and contact was lost in April 1980.

    Mock-up of the Zhurong rover in March 2021 – via AFP

    A return to Utopia Planitia is significant because Viking 2’s scientific mission uncovered interesting results during its analysis of the soil in the region during it’s stay on the planet. Viking 2 carried several biological experiments to aid in the search for life on Mars, and during one experiment, known as a Labeled Release (LR) experiment, Viking 2 injected a soil sample with a solution manufactured to influence any metabolism with micro-organisms that could be present within the soil.

    When Viking 2 performed the LR experiment, it returned results indicative that their were micro-organisms within the soil sample the spacecraft had collected from the surface. In the years since Viking 2, several theories have been thought of to provide a non-biological explanation for what Viking 2 could have found within the soil in Utopia Planitia, although many hope that the first return to the Planitia since Viking 2 hopes to definitively answer some of these 40 year old questions.

    Like all Mars landing attempts, a lot will need to go right if the Tianwen-1 lander is to safely touchdown in Utopia Planitia on Friday. If the CNSA is able to successfully pull it off, it will mark a breakthrough, not only for the growing space agency, but also for the wider space community.

    A successful landing of Tianwen-1’s lander will mark the first time an agency will have been able to safely land a spacecraft on the Martian surface on their first mission to the planet, an incredibly difficult and noteworthy achievement.

    (Lead render of orbiter/capsule separation via Mack Crawford for NSF)

    The post China prepares for country’s first Mars landing attempt with Tianwen-1 appeared first on NASASpaceFlight.com.

    Source : NASA More   

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    With Hubble, astronomers use UV light for first time to measure a still-forming planet’s growth rate

    In 2018, the exo-planet PDS 70b was observed using the Very Large Array.  It’s discovery… The post With Hubble, astronomers use UV light for first time to measure a still-forming planet’s growth rate appeared first on NASASpaceFlight.com.

    With Hubble, astronomers use UV light for first time to measure a still-forming planet’s growth rate

    In 2018, the exo-planet PDS 70b was observed using the Very Large Array.  It’s discovery instantly placed it at the top of observation requests and telescope time for one quite profound reason: the exoplanet was still forming.

    For the first time, a still-accreting planet had been discovered, providing astrophysicists a unique opportunity to study how planets form with real-time observations.  But one pesky problem existed: PDS 70b was far too close to its parent star for the usual exoplanet observational techniques to allow researchers to measure the planet’s growth rate.

    Now, for the first time ever using UV-band observations, a group of astrophysicists working with the Hubble Space Telescope’s Wide Field Camera 3 have produced the first measurement of PDS 70b’s current growth rate.

    The exoplanet in question orbits the star PDS 70 — a young, 10 million year old, K5 spectral type, low-mass T Tauri star located approximately 370 light-years from our solar system in the constellation Centaurus.

    A 140 AU-wide (1 Astronomical Unit , or AU, is equal to the average distance of Earth from the Sun: approximately 149 million kilometers) accretion disk around the star was confirmed in 2006, with an approximately 65 AU gap in that disk found in 2012.

    The gap instantly intensified interest in PDS 70, as large gaps in young star systems’ accretion disks are usually an indication of forming planets according to models of stellar system development.

    PDS 70b seen in this image from the Very Large Telescope. The planet stands out as a bright point to the right of the center of the image. (Credit: ESO, VLT, André B. Müller)

    In 2018, exoplanet PDS 70b was found in a 119.2 year orbit located approximately 20 AU from its parent star using the Very Large Telescope in Chile. The massive Jupiter-like planet, itself more than five times Jupiter’s mass, was too close to its parent star to be observed in the ways necessary to discern its current accretion (or growth) rate.

    “To study this specific planet, it needs UV information,” said Dr. Yifan Zhou, Postdoctoral Fellow, McDonald Observatory, University of Austin and lead author on the new study on PSD 70b’s accretion measurement, in an interview with NASASpaceflight.

    “Hubble is basically the only telescope that can do this work” due to the detail and precision of the observations,” noted Dr. Zhou.

    Using the orbital Hubble Space Telescope to observe the PDS 70 system gave Zhou et al. their best chance of seeing the exoplanet in the UV wavelength.  However, “the non-ideal part of Hubble compared to ground-based telescopes [is that] Hubble has a very small mirror.  It’s only 2.4 meters.”

    The smaller the mirror, the less sharp the image.  To account for this, the team employed multiple techniques — some for the first time with UV observations — to pull the exoplanet from the data while ensuring they were not detecting a false positive.

    “One very important concept here, the application we use in this observation is called angular differential imaging.  You take the image with different position angles, and your PSF, the point spread function structure is rotating with the telescope but your planet is staying in the same position,” related Dr. Zhou.

    “We can rotate the two images to have their point spread function match with each other, and when we subtract [them] from each other, your astrophysical signal, or planet signal, stays there and you remove all of your contamination from the star.”

    “So that’s a very important technique we used here.  It was developed in ground-based observations of exoplanets,” added Dr. Zhou.

    Typically, two angular differential imaging positions are used for such observations.  However, for this investigation, 18 different angles were required to gather the needed information. 

    To ensure the data didn’t return a false positive, interference showing an exoplanet where there isn’t one, Zhou et al. used artificial signals purposefully added to the images to ensure they were seeing a real exoplanet.   “At the very first stage, we [inserted] an artificial signal that we [knew was] there.  We inserted it into the images to see if after all these types of image processing we [could] recover [it],” said Dr. Zhou.  “And we recovered it, so that gave us additional confidence we were seeing a real signal.”

    Observations with Hubble occurred in two main wavelengths used for the final investigation in conjunction with various filters across 18 orbits.  Each orbit included ten, 120 second UV F336W band exposures and nine 20 second F656N (for hydrogen-alpha, or Hα, emission line) exposures using Wide Field Camera 3.

    In total, 21,600 seconds of observations in the F336W band and 3,240 seconds of information in the F656N band were collected.  After working with the data, Zhou et al. confirmed the detection of the exoplanet PDS 70b in UV. 

    For the first time, the UV information provided a clear look at the current accretion process taking place at PDS 70b.

    After its initial discovery, follow-up observations found PDS 70b likely had a circumplanetary disk of material… just as planetary formation models predicted it would.  The new UV investigation shed further light on the exoplanet’s disk, which itself proved useful in determining the processes still governing PDS 70b’s growth.

    The Hα emission lines from PDS 70b observed by Zhou et al. clearly showed active accretion as Hα emissions occur as material, following a forming planet’s magnetic field lines, flows into the planet and is heated in the process — creating a hot shock.

    Temperatures of hydrogen atoms in the gas and material being pulled into the planet therefore increase to the point where the atoms are excited and their single electron moves from the second to the third energy state.  When the electron falls back to the second energy level, an Hα emission is produced.

    However, a puzzling result from the analysis was the final measured accretion rate, which was found to be: M = 1.4 ± 0.2 x 10-8 MJupyr-1Put another way, under its current accretion rate, it would take PDS 70b one million years to accrete 1/100th of Jupiter’s mass.

    And that’s lower than super-Jupiter gas giant planet formation models predict.

    PDS 70b, seen by Hubble. (Credit: Joseph DePasquale, STScI)

    Zhou et al. are quick to caution that their calculations are a snapshot in time.  Additional observation, multi-decade, multi-century observations will reveal if accretion rates fluctuate greatly over time as planets go through growth spurts, so to speak, followed by periods of less active formation or if “Hα production in planetary accretion shocks is more efficient than [previous] models predicted, or [if] we underestimated the accretion luminosity/rate,” noted Zhou et al. in their paper published in April 2021 issue of .

     The team further noted, “By combining our observations with planetary accretion shock models that predict both UV and Hα flux, we can improve the accretion rate measurement and advance our understanding of the accretion mechanisms of gas giant planets.” 

    Moreover, as Dr. Zhou related to NASASpaceflight, additional observations will also reveal how much of the circumplanetary disk will accrete to the planet and how much of it will remain to form moons.

    “After the planet accretion is finished, there’s leftovers in the circumplanetary disk.  Those materials, they congregate.  Now, in terms of discovering them, my expectation is that it’s very, very challenging.”

    Not only is discerning an exomoon around an exoplanet incredibly difficult, alignment is also key.  “We need to have the planet aligned with the star and then the moon aligned with the planet,” related Dr. Zhou.

    While there are no confirmed exomoons to date, a few candidates have been proposed, and the potential – as technical advances – that PDS 70b could provide a close-to-home look at exomoon development remains.

    To this end, Dr. Zhou looks forward to the pending launch of the James Webb Space Telescope and its 6.5 meter mirror and infrared imaging capability.

    “For James Webb, we will have the first opportunity to probe the actual disk that is being accreted onto the planet.  And, actually, PDS 70b is a prime target for multiple James Webb programs that already have the guaranteed time observation.  So [those teams will] observe this planet in multiple wavelengths,” noted Dr. Zhou.

    The PDS 70 has two confirmed exoplanets, 70b and 70c, the latter of which was not seen in the data.

    (Lead image credit: NASA, ESA, STScI, Joseph Olmsted)

    The post With Hubble, astronomers use UV light for first time to measure a still-forming planet’s growth rate appeared first on NASASpaceFlight.com.

    Source : NASA More   

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