Efforts to build a major neutrino observatory in India cleared a legal hurdle on 2 November, when the country’s National Green Tribunal upheld environmental clearance for the long-planned project.

The clearance had been challenged by activists, who say that excavation for the facility will affect local wildlife and resources.

The planned 15-billion-rupee (US$206-million) experiment, called the India-based Neutrino Observatory, is set to be built under 1.2 kilometres of rock in the mountains of Tamil Nadu, a state in the nation’s south.

Physicists hope that the detector will help them to elucidate the relative masses of neutrinos, elusive particles produced when high-energy radiation known as cosmic rays strike the atmosphere, and whose behaviour has puzzled physicists for 20 years .

India’s government approved funding for the observatory in January 2015, but since then, the experiment has been subject to lengthy opposition from environmentalists and local politicians .

Before construction can begin, the project must also gain approvals from India’s National Board of Wildlife and from the Tamil Nadu Pollution Control Board. The facility is now unlikely to be completed before 2024.