{"id":32218,"date":"2025-09-02T09:20:51","date_gmt":"2025-09-02T13:20:51","guid":{"rendered":"https:\/\/stateofthenation.info\/?p=32218"},"modified":"2025-09-02T09:20:51","modified_gmt":"2025-09-02T13:20:51","slug":"if-made-of-solid-material-this-size-implies-that-the-mass-of-3i-atlas-is-a-million-times-larger-than-that-of-the-previous-interstellar-comet-2i-borisov","status":"publish","type":"post","link":"https:\/\/stateofthenation.info\/?p=32218","title":{"rendered":"

“If made of solid material, this size implies that the mass of 3I\/ATLAS is a million times larger than that of the previous interstellar comet 2I\/Borisov.”<\/b><\/h3>"},"content":{"rendered":"

Avi Loeb<\/p>\n

\n
\n
\"\"<\/picture><\/div>\n<\/div>
Deep images of 3I\/ATLAS, taken by the Gemini South telescope on August 27, 2025. The different panels show images from short to long wavelengths in the\u00a0u<\/em><\/strong>\u00a0(upper left),\u00a0g<\/em><\/strong>\u00a0(upper right),\u00a0r<\/em><\/strong>\u00a0(lower left) and\u00a0i\u00a0<\/em><\/strong>(lower right) spectral bands, centered on wavelengths of 0.365, 0.467, 0.616 and 0.747micrometers, respectively. The images show the first evidence for a teardrop shaped tail in the anti-Sun direction behind 3I\/ATLAS. (Credit:\u00a0B. Bolin et al. 2025<\/a>)<\/figcaption><\/figure>\n

On August 27, 2025, deep imaging of the interstellar object\u00a03I\/ATLAS<\/a>\u00a0by the\u00a0Gemini South<\/em><\/a>\u00a0<\/em>8.2-meter telescope \u2014 aided by the Gemini Multi-Object Spectrograph (GMOS), revealed a weak tail with a teardrop shape in the anti-Sun direction (reported\u00a0here<\/a>). At that time, 3I\/ATLAS was at a distance from Earth of 2.59 times the Earth-Sun separation. The Gemini South Observatory is located on a mountain called Cerro Pach\u00f3n in the Chilean Andes.<\/p>\n

The images were taken in the\u00a0u<\/em><\/strong>\u00a0(upper left),\u00a0g<\/em><\/strong>\u00a0(upper right),\u00a0r<\/em><\/strong>\u00a0(lower left) and\u00a0i\u00a0<\/em><\/strong>(lower right) spectral bands, centered on wavelengths of 0.365, 0.467, 0.616 and 0.747 micrometers, respectively. They show clear evidence for a teardrop shaped tail in the anti-Sun direction behind 3I\/ATLAS. The observed tail is about 30 arcseconds, or equivalently 56,400 kilometers long, pointing towards the South East. The coma is about 10 arcseconds or equivalently 18,800 kilometers wide, significantly more extended than its compact appearance in images of 3I\/ATLAS from early July 2025.<\/p>\n

Data collected on August 6, 2025 by the Webb Telescope (accessible\u00a0here<\/a>) confirmed the existence of a carbon dioxide (CO2) gas plume around 3I\/ATLAS with an order of magnitude lower levels of water (H2O) and carbon monoxide (CO), as reported earlier by the SPHEREx space observatory team (here<\/a>). SPHEREx mapped the CO2 plume out to 348,000 kilometers around 3I\/ATLAS. The inferred mass loss rates from 3I\/ATLAS are 130 kilograms per second for CO2, 6.6 kilograms per second for H2O and 14 kilograms per second of CO. The H2O mass loss rate is only 5% of the CO2 output, unlike expectations from a water-rich comet.<\/p>\n

It therefore comes as no surprise that the plume of gas around 3I\/ATLAS is shaped by the solar wind and the solar radiation pressure to a teardrop configuration. Before my morning jog at sunrise, I calculated today that the outer edge of the CO2 plume observed by SPHEREx, is bounded by the distance where the ram-pressure of the solar wind equals the ram-pressure of the CO2 outflow.<\/p>\n

As of now, it is unclear whether the scattering of sunlight in the glow and tail around 3I\/ATLAS is from dust particles or icy fragments made of CO2, CO and H2O that broke off the surface of the nucleus.<\/p>\n

\n
\n

Get\u00a0Avi Loeb\u2019s stories in\u00a0your\u00a0inbox<\/h2>\n<\/div>\n
\n

Join Medium for free to get updates from\u00a0this\u00a0writer.<\/p>\n<\/div>\n

\n
\n
<\/div>\n<\/div>\n
\n