Formation and evolution of the Solar System depletion period that brought the asteroid belt down close to its present mass is thought to have followed when Jupiter and Saturn entered a temporary 2:1 orbital resonance (see below). The inner Solar System's period of giant impacts probably played a role in the Earth acquiring its current water content (~6 kg) from the early asteroid belt. Water is too volatile to have been present at Earth's formation and must have been subsequently delivered from outer, colder parts of the Solar System. The water was probably delivered by planetary embryos and small planetesimals thrown out of the asteroid belt by
Solar hot water in Australia exported. Four of the original companies are still in business and the manufacturing base has now expanded to 24 companies. Water heating is the largest single source of greenhouse gas emissions from the average Australian home, accounting for around 28 per cent of home energy use (excluding the family car). The Australian government estimates that installing a climate friendly solar powered hot water system can save a family $300 to $700 off electricity bills each year. The solar hot water rebate program for financial year 2009 offered a $1600 rebate for the installation of solar powered hot water systems. The