Summary
Highlights
Building on last month's news, Dr. Smith discusses the interstellar comet 3i Atlas, discovered in July 2025 as the third such object passing through our solar system. On October 3rd, 3i Atlas passed close to Mars, allowing the European Space Agency's ExoMars Trace Gas Orbiter to capture images. Although the instruments were designed for bright, close-up targets, ExoMars successfully imaged the comet's fuzzy coma, which is thousands of kilometers across. The comet was 10,000 to 100,000 times fainter than ExoMars' usual targets, making any successful imaging a significant achievement. Future observations by the ISA Juice mission in November are anticipated to provide more detailed data.
JWST has delivered incredible images, including the largest star-forming region in the Milky Way, Sagittarius B2. A significant breakthrough was JWST's ability to spot a star before it exploded as a supernova (SN 2025PHT). Unlike the visible-light Hubble Space Telescope, JWST's infrared capabilities allowed it to peer through the dust-shrouded progenitor star that was invisible to Hubble for a period before its explosion. This enables better understanding of the types of stars that go supernova, their environments, and their final evolutionary stages. The star was found to be about 15 times the Sun's mass and in a carbon-rich environment.
Dr. Smith addresses the 'crisis in cosmology' or Hubble tension, where two primary methods of measuring the universe's expansion rate (Hubble Constant) yield conflicting results (74 km/s/Mpc from local galaxy measurements vs. 67 km/s/Mpc from cosmic microwave background models). The TD Cosmo collaboration introduces a new independent method using time delay cosmography and gravitational lensing of quasars. By measuring the time difference in light paths from a background quasar lensed by a foreground galaxy, they can directly determine absolute distances, bypassing the 'cosmological distance ladder' that might contribute to the tension. Their initial results from eight quasars give a value of 71.6 ± 3.6 km/s/Mpc, which lies in the middle of the conflicting values. While uncertainties are still large, further JWST observations are expected to provide more definitive conclusions.
Dr. Becky Smith introduces Night Sky News for October 2025, highlighting topics such as ExoMars and comet 3i Atlas, JWST's supernova discovery, and the crisis in cosmology. The segment then details upcoming celestial events for stargazers, including the tail end of the Orionids meteor shower, conjunctions of the crescent moon with Mercury and Mars (Oct 23-24), Saturn (Nov 1-2), and Jupiter (Nov 10). It also mentions a supermoon on November 5th, which will unfortunately wash out the Taurids meteor shower, and the peak of the Leonids meteor shower on November 17-18, expecting about 15 meteors per hour.