Confirmation of Recurrent Activity of Main-Belt Comet 456P/PANSTARRS (P/2021 L4)

Abstract We report observations from the Magellan Baade Telescope and Lowell Discovery Telescope on UT 2024 October 3 and 26, respectively, confirming for the first time that active asteroid 456P/PANSTARRS is recurrently active (exhibiting a short anti-solar tail on both dates, following previous observations of activity in 2021 when it was discovered), indicating that its activity is likely driven by the sublimation of volatile ice, leading us to consider it a main-belt comet (MBC). We also report observations from the Gemini South Observatory on UT 2023 June 15 in which the object appears inactive, where we measure an absolute magnitude of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>H</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>V</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mo stretchy="true">(</mml:mo> <mml:mn>17.5</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.1</mml:mn> <mml:mo stretchy="true">)</mml:mo> </mml:math> mag for the nucleus (assuming G V = 0.15), corresponding to an effective nucleus radius of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>r</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>n</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mo stretchy="true">(</mml:mo> <mml:mn>1.0</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.2</mml:mn> <mml:mo stretchy="true">)</mml:mo> </mml:math> km (assuming an albedo of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>p</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>V</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>0.05</mml:mn> <mml:mo stretchy="true">)</mml:mo> </mml:math> . 456P is now the 14th MBC for which recurrent activity has been observationally confirmed.