Two different questions
Mars already has a scientific answer to "where do we measure the planet from?" — the crater Airy-0 at 0°E has anchored Martian longitude since the IAU adopted it, and that continuity matters for mapping, missions, and navigation.
Mars does not yet have an answer to a different question: "where should the people living on Mars begin their day?" Mars Coordinated Time proposes that these two questions can be answered separately.
Why Arabia Terra
Arabia Terra is a vast region spanning the Martian equatorial and northern mid-latitude zone, containing some of the planet's oldest terrain and extensive evidence of its geological and hydrological history.
The 30°E offset
The initial MCT reference uses 30°E, producing a simple two-hour offset from Airy Mean Time.
A representative coordinate of 20°N, 30°E (Arabia Terra's central plain, ~0 km elevation) is used for solar-altitude calculations. This is a computational convenience, not a claim of territorial significance — see /research for how this differs from institutional precedent such as BIPM's lunar-time draft resolutions.
What this proposal does not do
- Does not alter the IAU Martian prime meridian (Airy-0 remains at 0°E)
- Does not change the Martian longitude system used by missions and cartography
- Does not establish an adopted international civil time standard
- Does not assert a fixed future settlement, epoch, or administrative boundary
Exact reference latitude, future settlement or observatory designation, epoch, and civil time-zone boundaries remain open for research and discussion.