TY - JOUR

T1 - Does It “Rain” Diamonds on Neptune and Uranus?

AU - Semerikova, Anna

AU - Chanyshev, Artem D.

AU - Glazyrin, Konstantin

AU - Pakhomova, Anna

AU - Kurnosov, Alexander

AU - Litasov, Konstantin

AU - Dubrovinsky, Leonid

AU - Fedotenko, Timofey

AU - Koemets, Egor

AU - Rashchenko, Sergey

N1 - The work was supported by the state assignment of IGM SB RAS. We acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. The research was carried out at PETRA III, P02.2 Extreme conditions beamline (proposals #I-20180048 and #I-20210753).

PY - 2023/3/16

Y1 - 2023/3/16

N2 - The methane phase diagram is extremely important to understand the physical properties of the ice giants─Uranus and Neptune. Several experimental studies using diamond anvil cells (DACs) combined with laser heating have reported the formation of diamond from methane at pressures of 10-80 GPa and temperatures above 2000 K, corresponding to the interiors of these planets. These results, however, are probably affected by the presence of metallic heat absorbers, widely used in all previously reported experiments and interacting with hydrogen at high pressure. In the present work, the effect of metallic heat absorbers on the decomposition of methane into diamond was studied at 20-95 GPa and 1300-3700 K using laser-heated DACs with platinum (as hydride-forming) and gold (as non-hydride-forming) metals. In the case of a platinum heat absorber, diamond formation was observed from 50 to 95 GPa near 2000 K simultaneously with platinum hydride formation. In contrast, in the case of a gold heat absorber, diamond formation was not observed below 95 GPa and 3700 K. Thus, the hypothesis of diamond precipitation in the Uranus and Neptune interiors should be reconsidered, taking into account the effect of metallic heater reactivity on the experimentally observed reactions.

AB - The methane phase diagram is extremely important to understand the physical properties of the ice giants─Uranus and Neptune. Several experimental studies using diamond anvil cells (DACs) combined with laser heating have reported the formation of diamond from methane at pressures of 10-80 GPa and temperatures above 2000 K, corresponding to the interiors of these planets. These results, however, are probably affected by the presence of metallic heat absorbers, widely used in all previously reported experiments and interacting with hydrogen at high pressure. In the present work, the effect of metallic heat absorbers on the decomposition of methane into diamond was studied at 20-95 GPa and 1300-3700 K using laser-heated DACs with platinum (as hydride-forming) and gold (as non-hydride-forming) metals. In the case of a platinum heat absorber, diamond formation was observed from 50 to 95 GPa near 2000 K simultaneously with platinum hydride formation. In contrast, in the case of a gold heat absorber, diamond formation was not observed below 95 GPa and 3700 K. Thus, the hypothesis of diamond precipitation in the Uranus and Neptune interiors should be reconsidered, taking into account the effect of metallic heater reactivity on the experimentally observed reactions.

KW - Neptune

KW - Uranus

KW - diamond

KW - ice giants

KW - methane

UR - https://www.scopus.com/inward/record.url?eid=2-s2.0-85147832877&partnerID=40&md5=75eaa3d1941867f759204cd37692dbd4

UR - https://www.mendeley.com/catalogue/e63722fd-6c24-3769-b5b8-caf77135163b/

U2 - 10.1021/acsearthspacechem.2c00343

DO - 10.1021/acsearthspacechem.2c00343

M3 - Article

VL - 7

SP - 582

EP - 588

JO - ACS Earth and Space Chemistry

JF - ACS Earth and Space Chemistry

SN - 2472-3452

IS - 3

ER -