Space Sunday: Mars, Starship and a meteor that flattened a city

September 10th, 2021: after successfully gather two samples from the rock dubbed “Rochette” (seen in the foreground, the bore holes clearly visible), the Mars 2020 rover Perseverance paused for a “selfie” using the WATSON imager mounted on the robot arm turret. Credit: NASA/JPL

It’s getting interesting on Mars. Jezero Crater, the home of the Mars 2020 mission is going through a change in seasons, bringing with it a drop in atmospheric density that is proving challenging for the Ingenuity helicopter, which recently completed its 13th flight.

The little drone was designed to fly in an atmosphere density around 1.2-1.5% that of Earth, but with the seasonal change, the average afternoon atmospheric density within the crater – the afternoon being the most stable period of the day for Ingenuity to take flight – has now dropped to around 1% that of Earth. This potentially leaves the helicopter unable to generate enough lift through its rotors to remain airborne.

The solution for this is to increase the rate of spin within rotors to something in excess of their nominal speed of around 2,500-2,550 rpm. However, this is not without risk: higher rpm runs the risk of a significant increase in vibrations through the helicopter that could adversely affect its science and flight systems. Also, depending on the wind, it could result in the propeller blades exceeding 80% of the Martian speed of sound. Sound this happen, the rotor would pick up enough drag to counter their ability to generate lift, leading to a mid-flight stall and crash.

To better evaluate handling and flight characteristics, therefore, the flight team are going back to basics an re-treading the steps taken to prepare Ingenuity for flight. This will see the propellers spun to 2,800 rpm with the helicopter remaining on the ground. Data gathered from this test will be used to make an initial assessment of blade speed required to get Ingenuity off the ground – believed to be somewhere between 2,700 and 2,800 rpm, and make an initial assessment of vibration passing through the helicopter’s frame. After this, it is planned to carry out a very simple flight: rise to no more than 5 metres, translate to horizontal flight for no more that a few metres, then land. Data from this flight – if successful – will then be used in an attempt to determine the best operating parameters for Ingenuity going forward.

The power of Perseverance’s camera: The lower image shows a true colour view of a feature dubbed “Delta Scarp”, captured by the rover’s MastCam Z system from a distance of 2.25 km. The upper picture shows details of the feature, as captured from the same distance, using the rover’s SuperCam instrument.. Credit: NASA/JPL

In the meantime, the Perseverance rover is continuing its work. Following the successful gathering of its first ample, the rover has been further revealing the power of its imaging systems, Mastcam Z and SuperCam, the two camera system mounted on its main mast.

Designed for different tasks, the two systems nevertheless work well together to provide contextual and up-close images of features the rover spies from distances in excess of 2 km away, allowing science teams to carry out detailed assessments before sending the rover to take a closer look. Also, in the wake of the sample gather exercise at the rock dubbed “Rochette”, NASA have provided a general introduction to two more of the rover’s instruments, which are mounted on the turret at the end of the rover’s robot arm. Catch the video below for more.

At the same time, and half a world away, the InSight mission Lander, despite suffering a severe degrading of its power capabilities as dust continues to accumulate on its circular solar arrays, has detected a  powerful Marsquake less than a month after detecting two equally powerful quakes originating at two different point under the planet’s surface.

All three were the latest in a long like of Marsquakes – also called “tumblors” – that have revealed much about the planet’s interior in the almost three years since InSight placed its seismometer on the planet’s surface, including the fact its core is larger than had been believed. The vast majority of the tumblors thus far detected have originated in the  Cerberus Fossae region of Mars, some 1,600 km from the lander. However, on August 25th, a quake measuring 4.1 magnitude was recorded with an epicentre just 925 km from the lander whilst marking it as the most powerful tremblor Insight had recorded (the previous record holder measure 3.7 – five times less powerful).

Captured in July 2021, this image shows InSight’s Seismic Experiment for Interior Structure (SEIS) instrument dome on the surface of Mars. This is the instrument that has been recording tremblors on Mars. Credit: NASA/JPL

But then on the same day, a second quake was detected, hitting 4.2 magnitude, marking it particularly powerful, given its epicentre was calculated to be 8,600 km from the lander, and possibly focused within Vallis Marineris, the “Grand Canyon of Mars. This was matched on September 18th by a further 4.2 magnitude quake – epicentre currently unknown. But what made this tremblor remarkable was its duration – almost 90 minutes! (By comparison, the longest recorded duration of an quake on Earth is under 5 minutes.) Exactly why and how such an event should or could last so long is unknown, and has the InSight science teams scratching their heads.

Did a Cosmic Event Give Rise to the Biblical Legend of Sodom and Gomorrah?

Tall el-Hammam was – up until 3,600 years ago – a thriving centre of life and commerce for an estimated 8,000 people. Located close to the Dead Sea in what is now modern day Jordan, the valley it occupied lay some  22 km west of the city of Jericho and was one of the most productive agricultural lands in the region before being practically deserted for some 500-700 years, the soil inundated with salts to the extent nothing would grow.

The location of the city has been subject to archaeological study since 2005, and researchers there have been struck by the curious nature of what little remains of the city: foundations with melted mud brick fragments, melted pottery, ash, charcoal, charred seeds, and burned textiles, all intermixed with pulverised mud brick and minerals that can only be produced under extremes of temperature and / or pressure. The more the city’s ruins were uncovered, the more the evidence pointed to some terrible calamity having befallen Tall el-Hammam and its surroundings, prompting the archaeologists to call in experts from the field of astronomy, geology, and physics. Their research has lead to the conclusion that the city was practically at the epicentre of a “cosmic airburst”.

Moment of detonation: an artist’s (rather mild) interpretation of the moment a 50m diameter chunk of rock travelling at 61,000 km/h detonated in the skies above Tall el-Hammam, Jordan, 3,600 years ago in a 15 megaton blast that obliterated the city in seconds. Credit: Allen West and Jennifer Rice, CC BY-ND

In short, 3,600 years ago, a piece of rock probably 50 metres across slammed into the atmosphere at 61,000 km/h. It survived the initial entry and fell to an altitude of approximately 4km above Tall el-Hammam before air resistance finally overcame its integrity. The result was a  15 megaton explosion that instant drove air temperatures to around 2,000ºC, enough to instantly flash-burn textiles, wood and flesh, and melt everything from swords and bronze tools to pottery and mud brick.

Seconds later, the shockwave from the explosion struck the city. Travelling at 1,200 km/h, it utterly pulverised what was not already aflame. Roughly a minute after the explosion, that same shockwave rolled over the city of Jericho, probably demolishing a good portion of its defensive wall and the buildings within it. That same shockwave also impacted the Dead Sea, potentially lifting vast amounts of salt water into the air, which rained back down over the valley, rendering it infertile for the next few hundred years, until rainfall could wash the salts out of the top soils.

The evidence for the cataclysm comes in multiple forms, from the melted pottery and mud brick through the clear evidence the city was pulverised in a manner that left a clearly defined “destruction layer” within the ruins, to the fact that within those ruins are deposits of shocked quartz, which are only formed when grains of sand are compressed with of force of 725,000 psi, and microscopic diamondoids, produced when carbon materials (e.g. plants, wood, etc.), are simultaneously exposed to massive extremes of temperature and pressure, and are a hallmark of ancient impact sites around the world.

A satellite image of the Middle East, showing the location of Tall el-Hammam on the northern coastal area of the Dead Sea. Satellite image via NASA

The ruins bring home the very real risk posed by near-Earth objects as they zap around the Sun, crossing and re-crossing Earth’s orbit. That a cosmic object also brought about the destruction of a small city and its 8,00 inhabitants raises the question of whether someone witnessed the event (obviously from many kilometres away) or its aftermath, and the telling and re-telling of the tale of destruction eventually morphed into the Biblical tale Sodom and Gomorrah, the two “cities of the plains” of the Dead Sea (and therefore potentially close to the site of Tall el-Hammam), supposedly destroyed by God in a rain of fire and rock falling from the sky.

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