The Orbital Index

The cosmic distance ladder. In order to estimate distances to astronomical objects (and attempt to solve the Hubble tension), astronomers use what is known as the cosmic distance ladder, a set of distance measuring techniques, each building off the previous technique. Comparatively close objects can be gauged via parallax, using shifts in apparent position caused by the Earth’s orbital movement to triangulate distance (as is done with exquisite accuracy by Gaia). More distant objects like galaxies can be measured by looking at the brightness of "standard candles" within them. Standard candles are objects whose actual luminosity is known based on physical constraints, so their distance can be gauged by comparing how bright they appear from Earth with their known actual luminosity. An example is Cepheid variables, stars whose luminosity is correlated with their pulsation periods. Over even more vast distances, Type Ia supernovae are used, again due to their predictable peak luminosity. There are many other techniques within the ladder. Similar to Cepheid variables, the predictable peak brightness of red giant stars at what is known as the tip of the red giant branch (TRGB) is often used. This technique is now even better, as a recent paper found that known acoustic oscillations of red giants at the TRGB can be used to more accurately determine their ages, which tells us how bright they should be, which, again, lets us infer their distance.

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The first Artemis lunar surface instruments. Paired with the recent LTVS announcement, NASA released plans for the first candidate instruments for astronauts to deploy when they return to the lunar surface as part of the Artemis III Deployed Instruments (A3DI) program. According to the agency, “the instruments will address three Artemis science objectives: understanding planetary processes, understanding the character and origin of lunar polar volatiles, and investigating and mitigating exploration risks.” Here’s a pdf that goes deep into Artemis’s science objectives. The first selected payload, the Lunar Environment Monitoring Station (LEMS), is focused on the seismographic exploration of the lunar south pole region, measuring moonquakes and characterizing the region’s crust and mantle. LEMS (not to be confused with the LEM) will have a lifespan of between three months and two years, and is envisioned to form the foundation of a network of lunar seismic monitoring stations. Lunar Effects on Agricultural Flora (LEAF) will observe the effects of the lunar environment on plant growth, particularly looking at photosynthesis, radiation exposure, and the impacts of partial gravity. LEAF hopes to return the first lunar-grown plant samples with Artemis III’s return trip—it will grow Brassica rapa, Duckweed (the smallest flowering plant), and Thale cress (the first plant to have its genome sequenced). If successful, samples will provide more useful data on off-world plant growth than Chang’e 4’s cotton seedling, which germinated and was photographed but then died due to plunging temperatures. The Lunar Dielectric Analyzer (LDA), a JAXA-funded instrument to measure the lunar regolith’s ability to propagate electric fields, will aid in our ability to find subsurface volatiles, especially ice. Artemis III is currently scheduled to fly in late 2026, and while final mission science manifests are subject to change, these three instruments are currently among the most likely to fly along with the first humans to land on the moon in 55+ years. Related: In exchange for the contribution of JAXA’s pressurized Lunar Cruiser rover to the Artemis program, the first non-American to walk on the Moon will be Japanese (unless China gets there first).

• A NYT piece ‘Overlooked No More: Henrietta Leavitt’ on Henrietta Swan Leavitt who worked as a (human) computer in the early 20th century cataloging stars. She discovered the period-luminosity relationship of Cepheid variable stars, now known as Leavitt's Law, which is the foundation of the cosmic distance ladder. She died in 1921 at age 53.
• EO for climate: Carbon Mapper data detects methane emissions from landfills in the US at levels significantly higher than reported (paper); satellite data debunk scam forest carbon credit projects in Australia; and, how GPS signals can be used to measure forest moisture content.
• “Fly, Fix, Fly,” a blog post on True Anomaly’s first mission that didn’t go as planned. Two of their Jackal autonomous orbital vehicles launched on Transporter-10, but only one of them contacted the ground, and that one established communications just two times. With so little data, the startup has been unable to determine the root cause of failure and is still investigating possible causes. Despite this, the company has found many silver linings (although goalpost-moving around the term “success” seems a bit rampant recently) and plans to implement significant changes in their next batch of Jackals—like decreasing weight for better maneuverability and payload capacity, improving ground testing, and enhancing autonomous functionality—with the goal of flying again within 12 months.
• That chunk of ISS battery debris that hit a Naples, FL home appears to have been a stanchion from the battery’s platform.
• Thales Alenia Space secured a €522M ($567M) ESA contract to restart the ExoMars rover program by developing the Mars Entry Descent and Landing Module (ELDM), which Russia would originally have provided. This module will transport ESA’s already-built Rosalind Franklin rover to the Martian surface in 2030 after launching on a NASA-funded vehicle in 2028.

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