為什麼科學家認為海王星和天王星不是冰巨行星？

University of California researchers suggest the planets' interiors may contain large magma oceans rather than water ice, leading them to propose the alternative term 'magma-ocean giants.' The two planets have never been studied up close beyond brief Voyager flybys, leaving their true internal structure uncertain.

NASA 有計畫進一步探索天王星嗎？

Yes. The international astronomy community is actively advocating for a dedicated Uranus orbiter mission, which is considered a top priority in the latest planetary science decadal survey, with hopes of launching within the coming decades.

這個新假說對行星科學有什麼影響？

If confirmed, reclassifying Neptune and Uranus as magma-ocean giants would significantly revise planetary science's classification system and could also change how scientists interpret similar-sized planets detected around other stars.

Scientists Suggest Neptune and Uranus May Not Be the 'Ice Giants' We Thought

A University of California research team is challenging the long-held classification of Neptune and Uranus as 'ice giants,' proposing instead that the two planets may be more accurately described as 'magma-ocean giants.' Because they remain the least-explored planets in the solar system, fundamental questions about their formation locations and internal structures are still unanswered.

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Highlights

A University of California research team proposes reclassifying Neptune and Uranus as 'magma-ocean giants' rather than 'ice giants,' based on the hypothesis that their interiors contain large magma oceans.

Neptune and Uranus are the least-explored planets in the solar system; NASA's Voyager missions conducted only brief flybys and no dedicated orbiter has ever studied either planet in depth.

Scientists currently cannot confirm where Neptune and Uranus formed in the early solar system, nor the true composition of their internal structures.

If the magma-ocean hypothesis is confirmed, it would overturn established planetary classification frameworks and alter the interpretation of similar exoplanets.

The international astronomy community is actively pursuing a dedicated Uranus orbiter mission as a top scientific priority for the coming decades.

Neptune and Uranus May Not Be 'Ice Giants' After All, Scientists Argue

For decades, Neptune and Uranus have been classified as the solar system's 'ice giants,' but a research team from the University of California is now challenging that designation, suggesting the two planets might be better described as 'magma-ocean giants.'

What Voyager Confirmed — and What It Didn't

Although NASA's Voyager flyby missions provided initial confirmation of the ice-giant classification, science outlet Gizmodo notes that Neptune and Uranus remain the least thoroughly explored planets in the solar system, having never been subjected to in-depth, systematic scientific investigation.

As a result, scientists are still unable to determine:

Where exactly the two planets formed in the early solar system
The true composition of their internal structures
The underlying causes of their distinctive physical characteristics

What the 'Magma-Ocean' Hypothesis Implies

The new hypothesis proposes that the interiors of both planets may harbor vast magma oceans, rather than the water-ice-dominated interiors traditionally assumed. If the hypothesis is substantiated, it would represent a significant disruption to planetary science's classification framework and could also reshape our understanding of similar planets discovered beyond the solar system.

The international astronomy community is currently pushing actively for a dedicated Uranus orbiter mission, hoping to resolve these mysteries within the coming decades.