While "who" typically implies a person, in this context, we are looking for objects or substances in the universe that predate our Sun. The answer, surprisingly, is Earth's water.
Explanation:
The water we find on Earth isn't newly formed. Instead, it's ancient, predating our solar system and even the Sun itself. This conclusion comes from studying the composition of water, specifically the ratio of deuterium (heavy hydrogen) to regular hydrogen.
- How Water Formed: Water molecules (H2O) can form in space within molecular clouds, which are vast regions of gas and dust. These clouds are the birthplaces of stars and planetary systems.
- Stellar Nurseries and Water's Journey: Before our Sun existed, the molecular cloud that birthed our solar system already contained water. This water was formed billions of years before the Sun ignited.
- Isotopic Ratios: Scientists can analyze the ratio of deuterium to hydrogen in water molecules. Water formed in cold, interstellar space tends to have a higher deuterium-to-hydrogen ratio than water formed in the warmer protoplanetary disk around a young star. The deuterium levels in Earth's water suggest it originated in these cold, interstellar clouds.
Therefore, the water we drink and that covers our planet is a relic from a period before the Sun existed, making it older than our star.
