<canvas id="densityChart" width="600" height="400"></canvas>

var densityCanvas = document.getElementById("densityChart");

Chart.defaults.global.defaultFontFamily = "Lato";
Chart.defaults.global.defaultFontSize = 18;

var densityData = {
  label: 'Density of Planet (kg/m3)',
  data: [5427, 5243, 5514, 3933, 1326, 687, 1271, 1638],
  backgroundColor: 'rgba(0, 99, 132, 0.6)',
  borderWidth: 0,
  yAxisID: "y-axis-density"
};

var gravityData = {
  label: 'Gravity of Planet (m/s2)',
  data: [3.7, 8.9, 9.8, 3.7, 23.1, 9.0, 8.7, 11.0],
  backgroundColor: 'rgba(99, 132, 0, 0.6)',
  borderWidth: 0,
  yAxisID: "y-axis-gravity"
};

var planetData = {
  labels: ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"],
  datasets: [densityData, gravityData]
};

var chartOptions = {
  scales: {
    xAxes: [{
      barPercentage: 1,
      categoryPercentage: 0.6
    }],
    yAxes: [{
      id: "y-axis-density"
    }, {
      id: "y-axis-gravity"
    }]
  }
};

var barChart = new Chart(densityCanvas, {
  type: 'bar',
  data: planetData,
  options: chartOptions
});