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NASA’s Parker Solar Probe
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On December 24, 2024, NASA’s Parker Solar Probe achieved an extraordinary milestone by approaching within 6.1 million kilometers of the Sun’s surface—closer than any spacecraft before it.
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- This achievement was the result of a seven-year journey, with the probe continuing its mission by making additional close approaches on March 22 and June 19 of this year.
Observing the Sun
- Primary Source of Energy: As the primary source of energy for life on Earth, the Sun generates its energy through nuclear fusion in its core.
- It also possesses highly dynamic magnetic fields that, when rearranged suddenly, lead to powerful eruptions known as solar flares.
- The Sun’s outermost layer, the corona, expels vast amounts of energetic particles, including electrons, protons, and heavy nuclei, traveling at speeds of up to 900 km/s.
- Coronal Mass Ejection: When these particles surge towards Earth in an event called a coronal mass ejection, they can trigger solar storms.
- Such storms may disrupt electric grids, interfere with telecommunications, damage satellite instruments, and even affect the ozone layer.
- The Indian Space Research Organisation (ISRO) launched the Aditya-L1 probe, currently positioned 150 million kilometres from the Sun, to complement Parker’s findings.
Advanced Heat Shield Technology
- The Parker Solar Probe is named in honor of Eugene Parker, who predicted the existence of the solar wind—an outward flow of charged particles from the Sun in all directions.
- Launched in August 2018 aboard a Delta IV rocket from Cape Canaveral, the probe reached an astounding speed of 692,000 km/h.
- To withstand the Sun’s intense heat, the probe is equipped with an advanced heat shield—an 8-foot-wide, 4.5-inch-thick carbon-carbon composite capable of enduring temperatures of up to 1,370º C while weighing only 73 kg.
- Designed by researchers at the Johns Hopkins Applied Physics Laboratory, the shield features a carbon composite foam core sandwiched between two carbon plates, with its Sun-facing surface coated in white ceramic paint to reflect solar radiation.
- Remarkably, just a few meters behind the shield, the temperature drops to a manageable 29º C, allowing the probe’s scientific instruments to function without the need for special cooling measures.
- The probe also includes two sets of solar power arrays—one positioned in the shield’s shadow to power scientific instruments and another exposed to sunlight, equipped with a fluid cooling system to sustain the probe during its closest approaches.
Navigating the Solar System
- Surprisingly, the biggest challenge for the Parker Solar Probe wasn’t the Sun’s heat but its immense gravitational pull.
- To prevent the probe from plunging directly into the Sun, scientists devised an intricate flight path.
- Initially, a route involving Jupiter’s gravity to decelerate the probe was considered but ultimately discarded due to the excessive travel distance.
- Instead, the final trajectory used gravity assists from Earth and Venus, enabling the probe to spiral closer to the Sun over time.
- This approach has allowed it to spend more than 2,000 hours flying through the corona and conducting 24 passes along the solar equator.
Scientific Exploration and Discoveries
- The Parker Solar Probe is outfitted with four key scientific instruments:
- FIELDS: Measures the Sun’s electric and magnetic fields.
- ISoIS (Integrated Science Investigation of the Sun): Observes energetic particles responsible for solar storms.
- SWEAP (Solar Wind Electrons Alphas and Protons): Analyses properties of the solar wind.
- WISPR (Wide-Field Imager for Parker Solar Probe): Captures images of the corona during flybys.
- In April 2021, Parker made history by becoming the first spacecraft to cross the Sun’s Alfvén surface—the boundary beyond which solar wind no longer influences the Sun’s surface.
- This was confirmed by data from the FIELDS and SWEAP instruments.
- Additionally, a specialised instrument called the Faraday cup, which lies outside the heat shield, measures the density of charged particles in the solar wind.
- Constructed from a molybdenum alloy with a melting point of 2,349º C, it withstands the Sun’s extreme conditions to provide crucial data.
Breakthrough Discoveries in Solar Physics
- Previously, scientists assumed that space dust, formed by weathering cosmic rocks, was uniformly distributed throughout the solar system.
- However, Parker detected regions near the Sun that are free of dust.
- The probe also observed magnetic switchbacks—sections of the solar wind where the magnetic field unexpectedly bends backward.
- One of the most significant questions in solar physics is why the Sun’s surface is relatively cool at approximately 6,000ºC, while the corona is exponentially hotter at around 1 million degrees.
- Parker’s findings suggest that Alfvén waves—plasma oscillations driven by magnetic forces—may hold the key to solving this mystery.
