Last night a 900 foot wide asteroid made the latest in a series of close approaches towards Earth.
There is a chance it could collide with the Earth in 2036, the biggest threat would be if it fell on land mass.
Speaking to ITV Daybreak, Dr Maggie Aderin-Pocock said if it hits a city it would cause devastation.
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At times a little fair weather cloud may bubble up - and there will be a fairly brisk southeasterly breeze - but it will still feel hot.
Analysis of data from hospitals in England showed patients were waiting longer for ambulances, treatment and admission.
She told reporters: "I don't think it's fully sunk in how really bad that could have been, I know it's not the right decision."