{"id":235,"date":"2023-05-26T19:41:00","date_gmt":"2023-05-26T19:41:00","guid":{"rendered":"https:\/\/www.hyades.oa.uj.edu.pl\/esa\/?page_id=235"},"modified":"2026-11-02T23:24:45","modified_gmt":"2026-11-02T23:24:45","slug":"new-water-reservoirs","status":"publish","type":"page","link":"https:\/\/www.hyades.oa.uj.edu.pl\/esa\/new-water-reservoirs\/","title":{"rendered":"New water reservoirs"},"content":{"rendered":"

The classical paradigm divides minor bodies in the Solar System into comets and asteroids, distinguished by their orbital properties and the presence or absence of sublimation-driven activity. However, this picture became blurred when comet-like activity was discovered in 133P\/Elst-Pizarro in 1996, eventually leading to the recognition of Main-Belt Comets (MBCs)\u2014small objects with comet-like comae and tails but asteroid-like orbits (Hsieh & Jewitt 2006). Understanding their activity has far-reaching implications for the distribution of water and the evolution of our Solar System.<\/p>\n

MBCs belong to the broader population of active asteroids, whose dust emission can also result from impacts, rapid rotation or fragmentation. The defining feature of an MBC is activity driven, at least partly, by sublimating ice. Recurrent activity near perihelion has long provided strong evidence for this mechanism. Prolonged dust emission in 313P\/Gibbs, 358P\/PANSTARRS and 288P also supports sublimation, whereas the fragmentation of P\/2013 R3 illustrates how rotational disruption can complicate the interpretation of apparently cometary behaviour (Jewitt et al. 2014, 2015).<\/p>\n

Searching for gas: the limitations of indirect tracers<\/strong><\/p>\n

In ordinary comets, gas is commonly detected through emission produced when atoms and molecules interact with solar radiation. One of the most widely used optical tracers is CN, whose prominent violet band lies near 388 nm. Historically, however, searches for CN in MBCs yielded only upper limits, even with large telescopes such as Keck, VLT, Gemini and GTC. These included Q(CN) < 1.8\u00d710\u00b2\u00b3 molecules s\u207b\u00b9 for 313P, < 1.5\u00d710\u00b2\u00b3 molecules s\u207b\u00b9 for 358P, and < 1.4\u00d710\u00b2\u00b3 molecules s\u207b\u00b9 for 259P\/Garradd (Jewitt et al. 2015; Hsieh et al. 2013; Jewitt et al. 2009).<\/p>\n

CN production can be converted into an estimated water production rate by adopting a typical cometary abundance ratio, often Q(H\u2082O)\/Q(CN) \u2248 350. However, water and CN trace different chemical pathways, and MBCs need not share the composition of ordinary comets. A stringent CN upper limit therefore does not necessarily provide an equally stringent constraint on water.<\/p>\n

Direct searches initially remained unsuccessful. Herschel established Q(H\u2082O) < 4\u00d710\u00b2\u2075 molecules s\u207b\u00b9 for 176P\/LINEAR and < 7.6\u00d710\u00b2\u2075 molecules s\u207b\u00b9 for 358P\/PANSTARRS (de Val-Borro et al. 2012; O\u2019Rourke et al. 2013). VLT searches for water\u2019s photodissociation products in 358P yielded a comparable limit of approximately 8\u00d710\u00b2\u2075 molecules s\u207b\u00b9 (Snodgrass et al. 2017). These constraints applied to particular objects and observing epochs, rather than establishing a universal ceiling on MBC water production.<\/p>\n

\"\"

First water detection on Main Belt Comet 238P\/Read.<\/p><\/div>\n

JWST: finally detecting the water<\/strong><\/p>\n

The breakthrough came with JWST observations of 238P\/Read in September 2022. Its spectrum revealed unambiguous water-vapor emission near 2.7 \u03bcm, providing the first direct spectroscopic confirmation of water outgassing from an MBC (Kelley et al. 2023). A second detection followed in 358P\/PANSTARRS (Hsieh et al. 2025), and results published in 2026 confirmed water in 133P\/Elst-Pizarro (Hsieh et al. 2026). After decades of searching, sublimation in these objects had finally been confirmed.<\/p>\n

Water was detected in three of these four objects. Intriguingly, 457P showed clear dust activity without detectable water emission, suggesting differences in ice availability, dust-to-gas ratio or the mechanisms contributing to dust release (Noonan et al. 2026).<\/p>\n

A hidden reservoir waiting to be mapped<\/strong><\/p>\n

These detections confirm that small bodies in the Main Belt still contain water ice capable of sustaining cometary activity. Long-term survival generally requires ice to remain protected beneath an insulating surface layer, becoming accessible when impacts or other surface disturbances expose it.<\/p>\n

The challenge now is to determine how widespread this surviving ice is and how its abundance varies across the asteroid belt. JWST has demonstrated that water measurements are possible, but the sample remains small. A dedicated instrument capable of surveying water and its photodissociation products in many more objects would help turn these pioneering detections into a systematic map of the Main Belt\u2019s hidden ice\u2014potentially the nearest long-lived reservoir of cometary water to Earth.<\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

The classical paradigm divides minor bodies in the Solar System into comets and asteroids, distinguished by their orbital properties and the presence or absence of sublimation-driven activity. However, this picture became blurred when comet-like activity was discovered in 133P\/Elst-Pizarro in 1996, eventually leading to the recognition of Main-Belt Comets (MBCs)\u2014small […]<\/p>\n","protected":false},"author":4,"featured_media":252,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_monsterinsights_skip_tracking":false,"footnotes":""},"class_list":["post-235","page","type-page","status-publish","has-post-thumbnail","hentry"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t