Astronomy & Space Technology

Context: Venus is much drier than Earth, and scientists have been trying to figure out why. They believe that Venus once had a lot of water, but it has since escaped into space.

Venus

• More than four billion years ago, Venus had enough water to cover its surface with an ocean 3 km deep. Today, the planet only has enough for this ocean to be 3 cm deep.

Water loss mystery from Venus: 

• One theory is that the water from Venus was lost due to the Sun's heat and ultraviolet radiation.
• A new study suggests that a chemical reaction involving a molecule called HCO+ may be responsible for some of the water loss. This reaction breaks down water molecules and allows hydrogen atoms to escape into space. 
  • The study's authors say that this reaction could have doubled the rate at which Venus lost water. They also say that the reaction could have been going on for billions of years.
  • However, there is no direct evidence that HCO+ exists in Venus's atmosphere. Hence, future missions to Venus should look for HCO+.

Significance in Planetary Atmospheres:

• Hydrogen Escape Mechanism: The neutral hydrogen atoms produced in this reaction are energetic enough to escape the planet’s gravity, leading to a gradual loss of hydrogen from the atmosphere.
• Water Loss: Since water (H2O) is composed of hydrogen and oxygen, the loss of hydrogen atoms contributes directly to the depletion of water on a planetary scale. (As Oxygen atoms would not have sufficient Hydrogen atoms to combine to form Water)

Facts about Venus:

• Venus has a solid surface by virtue of being one of the 3 inner planets besides Mercury and Earth. It is nearly the same size as the Earth.
• The atmosphere of Venus is composed of 95% carbon dioxide and thus has a high greenhouse effect.
• Surface pressure on Venus is about 90 times that on Earth while surface pressure on Mars is 1/100th of that on Earth.
• NASA’s image data from the Magellan spacecraft's visit to Venus has revealed evidence of volcanic activity on it. Sulphur compounds make up about 0.015% due to volcanic eruptions and thus hot Sulfuric acid clouds that envelop Venus. About 80% of the surface of Venus is composed of flat plains of volcanic origin.
• Its rotation period is longer than its orbital period. (Rotation on its own axis – 243 days, Orbital period around the sun - 224.7 days) The planet has retrograde rotation, meaning it spins in the direction opposite to the direction in which it orbits the Sun.
• Due to the slow rotation of Venus it has no global magnetic field. (Earth’s magnetic field is due to rotation of iron core).

Upcoming Venus missions:  

• Shukrayaan (ISRO, India), DAVINCI mission (NASA, USA), VERITAS orbiter (NASA, USA), EnVision mission (European Space Agency).
  • Shukrayaan-1 (2024): Expected to be launched in 2028. This orbiter will study the planet's atmosphere, surface, and ionosphere.
  • NASA's DAVINCI (Deep Atmosphere Venus Investigations of Noble gases, Chemistry, and Imaging) mission will study Venus from above its clouds down to its surface, investigating how the planet and its dense atmosphere formed and evolved over the past 4.5 billion years. Tentatively scheduled to be launched in June 2029 and would enter the Venusian atmosphere in June 2031. 
  • VERITAS: NASA's VERITAS (Venus Emissivity, Radio Science, InSAR, and Spectroscopy) mission is expected to be launched in 2031. VERITAS will use a suite of seven instruments to study the surface and atmosphere of Venus.
  • EnVision: The European Space Agency (ESA)'s EnVision mission is planned for launch in the early 2030s. EnVision will study the atmosphere, surface, and interior of Venus.

Context: Indian Space Research Organisation (ISRO) announced that its PSLV Orbital Experimental Module-3 (POEM-3) re-entered the Earth's atmosphere in March 2024 without leaving any debris in orbit.

Major Highlights: 

• Mission launch: The PSLV-C58 mission was launched on January 1, 2024.
• Primary Mission: The mission's main objective was to deploy XPoSAT satellite into the intended orbit of 650 km, which it successfully accomplished.
• POEM-3: After deploying the satellite, the leftover part of the PSLV rocket, the terminal stage (fourth stage), was not discarded. Instead, it was ingeniously repurposed into a stabilised platform named POEM-3 (PSLV Orbital Experimental Module-3).

PSLV Orbital Experimental Module (POEM):

• Developed by: Vikram Sarabhai Space Centre (VSSC).
• POEM is an experimental mission or space platform to perform in-orbit experiments using the final, and otherwise discarded, stage of ISRO’s PSLV.
  • PSLV is a four-stage rocket where the first three spent stages fall back into the ocean, and the final stage (PS4) — after launching the satellite into orbit — ends up as space junk. 
  • In POEM, the spent final stage will be utilised as a stabilised platform to perform experiments. 
• POEM has a dedicated Navigation Guidance and Control (NGC) system which will act as the platform’s brain for attitude stabilisation with specified accuracy. 
• POEM will derive its power from solar panels mounted around the PS4 tank, and a Li-Ion battery. It will navigate using four sun sensors, a magnetometer, gyros & NavIC.

Zero orbital debris milestone:

• Deorbiting POEM-3: To ensure POEM-3 would not remain as space junk, its orbit was lowered from a high altitude of 650 km to a much lower one at 350 km. This significantly reduced the time it took for POEM-3 to re-enter Earth's atmosphere and burn up.
• Passivation: To further minimise risks, any leftover fuel on POEM-3 was eliminated in a process called passivation. This reduced the chance of an accidental explosion during re-entry that could create debris.
• Zero-Debris Goal Achieved:  On March 21, 2024, POEM-3 re-entered the earth’s atmosphere, meeting its fiery end. Due to the well-planned deorbiting and passivation manoeuvres, the PSLV-C58/XPoSat mission resulted in practically zero debris left behind in Earth's orbit. This is a significant achievement in space sustainability, reducing the potential hazards of space debris for future missions.

Space Debris: 

• Space debris in the low earth orbit (LEO) mainly comprises pieces of spacecraft, rockets, and defunct satellites, and the fragments of objects that have deteriorated explosively as a result of anti-satellite missile tests.
• This debris often flies around at high speeds of up to 27,000 kilometres per hour. Due to their sheer volume and momentum, they pose a risk to several space assets.
• With the rise in the number of satellites in orbit around the earth, space debris has become a pressing issue, particularly in the Low Earth Orbit (LEO).
  • Currently, there are 7,000 operational satellites orbiting the earth at different altitudes along with millions of pieces of space debris.
  • According to ISRO’s Space Situational Assessment report 2022, the world placed 2,533 objects in space in 179 launches in 2022, up from 1860 objects in 135 launches in 2021.
• As more communication satellites/constellations are launched and more anti-satellite tests are conducted, more on-orbit breakup and collisions occur, producing smaller and smaller fragments in orbit. 
  • The number of space objects (debris or functional equipment) greater than 10 cm in size in LEO is expected to be about 60,000 by 2030, per ISRO estimates.
• Space debris also leads to two major risks – it creates unusable regions of the orbit due to excessive debris, and leads to the ‘Kessler syndrome’ – creation of more debris due to cascading collisions resulting from one collision.

How are space agencies dealing with debris?

• Currently, there are no international space laws pertaining to LEO debris.
• However, most space-exploring nations abide by the Space Debris Mitigation Guidelines 2002 specified by the Inter-Agency Space Debris Coordination Committee (IADC), which the U.N. endorsed in 2007.
• The U.S. Space Command tracks and catalogues space debris larger than 10 centimetres in LEO and larger than 0.3-1 metres in geosynchronous orbit (GEO).

Context: An international team of scientists, including from India, has discovered strong evidence indicating the presence of ozone on Jupiter’s moon, Callisto.

Importance of Ozone: 

• Ozone molecule is composed of three oxygen atoms bonded together.
• The ozone layer is found in the lower part of the earth’s stratosphere, around 15–35 km above ground, and serves as a shield as it completely absorbs ultraviolet-B and ultraviolet-C radiation.
  • Ultraviolet-B (wavelengths 290–320 nanometres) and ultraviolet-C (100-280 nanometres) can damage DNA, trigger mutations, inhibit plant growth and increase the risk of skin cancer and cataracts in humans.
• Without the ozone layer, UV-radiation levels would be much higher on Earth’s surface, rendering it uninhabitable for many species and disrupting entire ecosystems.
• Rationale of the study: Scientists are currently studying various celestial bodies in the Solar System that show signs of ozone, suggesting the existence of stable atmospheric conditions and, by extension, their possibility of hosting life. 

Callisto and its unique environment: 

• Callisto is one of Jupiter’s largest moons and the third-largest moon in the Solar System after Ganymede (Jupiter’s moon) and Titan (Saturn’s moon).
• Callisto is primarily composed of water ice, rocky materials, sulphur dioxide, and some organic compounds. These substances make the moon a potential candidate for supporting life in the solar system beyond the earth. 
• Callisto’s surface is heavily cratered, indicating a long history of being struck by asteroids and comets. 
• It lacks the extensive seismic activity, which is present in some of Jupiter’s other moons like Europa.
• It has relatively few geological features which suggest that Callisto’s surface is geologically inactive or relatively stable for a long time. This stability could be vital to preserve any subsurface ocean or potential habitats beneath the icy crust.

The Experiment: 

• The Scientists modelled the surface of Callisto icy surface conditions in a lab, and analysed the chemical reactions occurring on the surface of Callisto when sunlight hits its surface (caused by ultraviolet radiation).
  • The experiments were conducted at the National Synchrotron Radiation Research Centre (NSRRC) in Taiwan, which provided access to high-energy radiation sources required to recreate the radiation coming from the Sun.
  • To do this, the researchers used vacuum ultraviolet photons (of wavelength 137.7 nanometres), which mimic the solar radiation that reaches the moon’s surface.
  • To model the surface of Callisto, the researchers placed a substrate of lithium fluoride in a chamber with very low pressure. This environment recreated conditions similar to those found in outer space.
  • The sulphur dioxide ice samples were deposited onto the substrate, setting the stage for the final step: observing the absorption spectrum.
    • The absorption spectrum is the unique fingerprint of a substance.’
    • It shows the wavelengths of light it absorbs, providing insights into its composition and properties.
  • Finally, they irradiated the ice with vacuum-ultraviolet photons and recorded its ultraviolet absorption spectrum during and after the irradiation using a photomultiplier tube detector. 
• The ultraviolet absorption spectrum revealed the formation of ozone after the sulphur dioxide ice samples were irradiated.
• The researchers also compared their experimental data with data collected by the Hubble Space Telescope, which had also suggested the presence of sulphur dioxide and ozone on the surface of Callisto in 1997.

Significance: 

• The discovery of ozone on Callisto suggests the presence of oxygen, which in turn is a fundamental ingredient required for the formation of complex molecules required for life such as amino acids. 
• The investigation into the chemical evolution of ‘SO2 astrochemical ice’ (ice primarily composed of sulphur dioxide (SO2) in the presence of ultraviolet irradiation) would shed light on the chemical processes and composition of the surface of Callisto. 
• Hence, the findings would help in understanding Callisto’s environment and the potential habitability of icy moons in the Solar System.

About International Astronomical Union:

• The International Astronomical Union (IAU) is a non-governmental organisation that works to advance astronomy. It was founded in 1919 and is headquartered in Paris, France.
• Primary functionsof IAU:
  • Promoting astronomical research, communication, education, and development through international cooperation.
  • Assigning designations and names to celestial bodies (stars, planets, asteroids, etc.) and any surface features on them. 
  • Establishing standards for astronomical observation and data. 
• The IAU is a member of the International Science Council (ISC). It has over 12,000 individual members from more than 100 countries.

Planetary Nomenclature:

• Planetary nomenclature is used to uniquely identify a feature on the surface of a planet or satellite so that it can be easily located, described, and discussed.
• IAU is the internationally recognised authority for assigning names to planetary surface features. It follows some rules and conventions to do so.
  • The IAU’s Rule 9 states: “No names having political, military or religious significance may be used, except for names of political figures prior to the 19th century.”

Key Facts:

• Recently, IAU’s working group for Planetary System Nomenclature has approved the name “Statio Shiv Shakti” for the landing site of Chandrayaan-3’s Vikram lander. 
• Recently, IAU has named an asteroid after an Indian astro-scientist Prof. Jayant Murthy for his contributions to astronomy, especially to the New Horizons mission. His team’s endeavour to observe ultraviolet background radiation in the outer Solar System, where the interference from the Sun and interplanetary medium is minimal, have played a crucial role in broadening understanding of cosmic phenomena.
  • New Horizons is an interplanetary space probe launched by NASA's in 2006. 
  • It is the first spacecraft to explore Pluto, flying by the dwarf planet and its moons on July 14, 2015. 
  • In early 2019, New Horizons flew past its second major target – Arrokoth, the most distant object ever explored up close. (Arrokoth is a trans-Neptunian object located in the Kuiper belt)

Asteroid Belt:

• Asteroids are rocky remnants from the early formation of our solar system (about 4.6 billion years ago) that mainly orbit the Sun between Mars and Jupiter.
• The asteroid belt is a nearly flat ring that contains millions of asteroids, ranging in size from less than 10 metres to 530 kms (The largest asteroid is Ceres, which is about one-quarter the size of Earth’s moon).